of over 7,000,000 square feet of factory space built by the development corporations , about 20 per cent represents extensions built after the firms had become established . it is the policy of the corporations to charge full rack-rents or ground rents for their factories or industrial sites ; and rents vary considerably according to the demand for factory accommodation . the average gross return on established industrial estates ranges from 7 to 9 per cent of the capital expenditure on land , site works and buildings . manufacturing industry affords employment to large numbers of non-manual as well as manual workers . an analysis made by Crawley development corporation in 1958 , after collating replies from fifty-eight manufacturing firms employing over nine thousand staff , showed that 5 per cent of the staff were classed as managerial and administrative , 11 per cent as technical or employed in research and 19 per cent as clerical . there is no reason to suppose that this pattern is peculiar to Crawley . the development corporations have aimed at a varied pattern of industry , offering a reasonable choice of employer as well as choice of occupation for men , women and school-leavers , with due regard to the industries already established in their towns . inevitably engineering , including the motor vehicle and aircraft industries , predominates in all the London new towns since these are among the industries which have expanded most during the last ten years in the country generally . of those at present employed in manufacturing industry in the eight London new towns about 40 per cent are employed in engineering and electrical goods manufacture - the proportion employed in both these groups combined varies from about 30 per cent in Welwyn to 85 per cent in Stevenage and 90 per cent in Hatfield . these figures are much higher than the national averages , and may be thought to indicate a lack of balance in some of the towns . on the other hand these groups offer fairly varied opportunities of skilled employment and are highly diversified as regards products , markets and methods of manufacture . consumer goods industries such as the manufacture of food and drink , tobacco , clothing and footwear are under-represented in the new towns generally though not in Basildon and Welwyn . the following table indicates the size of the firms , some of them occupying more than one factory , introduced or sponsored by development corporations in the new towns : the overall average for the factories sponsored by development corporations is about 170 employees per firm , and the average for each of the London new towns is roughly the same except at Hatfield , where it is much lower , and Stevenage , where it is much higher . the position at Stevenage is accounted for by the presence of one firm with 3,700 employees and two others with over 1,000 employees . about 32 per cent of all the workers employed in factories sponsored by the development corporations are employed by the eleven largest firms and about 23 per cent by the next group of firms employing between five hundred and one thousand workers . in factories sponsored by the London new town development corporations the proportion of female employees , expressed as a percentage of all employees , varies from 23 per cent in Welwyn Garden City and 24 per cent in Hemel Hempstead to 35 per cent in Basildon and 55 per cent in Hatfield with an average of about 30 per cent - rather less than in the country as a whole . the figures for Corby and Peterlee ( where the prime need so far has been to provide employment for women and girls ) are 82 per cent and 74 per cent respectively . shops . shopping provision in the new towns has generally been based on an estimated need of about eight shops for every thousand people , this being considered sufficient to allow for shoppers coming into the town from surrounding areas . distribution over the town as a whole varies , the smaller towns tending to rely mainly on the town centres with a few pantry shops in the neighbourhoods and the larger ones providing neighbourhood centres of up to thirty or more shops at the heart of the residential areas , as well as small sub-centres in outlying districts . some development corporations have sought to attract private investors by leasing part of the shopping area to companies experienced in commercial development who have undertaken the building and letting of the shops . but corporations have generally found it more satisfactory to build themselves , leasing the shops direct to traders , with breaks in the lease to enable rents to be increased in scale with the rising prosperity of the town . this control over lettings also secures a balanced distribution of the type of shop , to meet the convenience of shoppers , and a reasonable degree of economic security for the individual shopkeeper . timing has proved an important factor in the success of the shops . too many at the start may not provide a living for the traders , but too few may result in failure to attract custom and the habit of dependence on mobile shops , essential in the early stages , may be slow to break if carried on too long . the establishment of open markets in the town centres has helped to bring custom to the shops and the initial fears of some of the shopkeepers that their trade would suffer have proved unfounded . shopping on two levels has been introduced in a number of towns and has added to the interest of the town centre . all types of trader have been encouraged , from the large departmental store to the small shoe-mender , with banks specially sited on corners or in separate courts to avoid breaking into the shopping frontage . as in the case of factories and industrial sites , the corporations &apos; policy has been to charge full commercial rents for their shops and shopping sites . the cost of town centre development has been very high in some cases with large paved areas and pleasant amenities and decorative features . the gross return on capital expenditure on town and neighbourhood shopping centres ranges from 6 to 13 per cent . it is to their successful industrial and commercial development that the corporations must look to recoup the high costs of main sewerage and drainage , main roads and other special development expenditure . service industry . in the early stages of a new town most of the working population are employed in manufacturing or basic industry . in the London new towns it is estimated that between 60 per cent and 70 per cent are so employed ; in the provincial new towns the figure is somewhat higher . employment in services of one kind or another may be expected to increase as the towns approach maturity : indeed , in the country generally the proportion of people so employed is growing steadily . these services develop at their own pace in response to local demand , however , and little can be done to stimulate them . office employment . in practice it has not proved possible as yet to attract head offices and administrative and research establishments including sections of government departments and other public offices on the scale needed to establish the character of the town from the outset as one of diverse and balanced social composition as recommended by the Reith committee . except at Hemel Hempstead , large office organisations have until quite recently shown little interest in the new towns , probably because of the difficulty in the early years in recruiting suitable staff , especially junior staff , locally . there is evidence of greater interest today , with nearly half a million square feet of office space under construction - almost as much as the total area so far completed . this interest is likely to grow as employers become aware of the advantages of setting up offices in towns with a young and growing population and excellent schools and technical colleges . towards the end of the year the Minister wrote personally to some two hundred chairmen of companies with large offices in central London , drawing their attention to the opportunities offered by the new towns . the development corporations have provided office accommodation ( in addition to that included in factory premises ) in the form of buildings specially designed to meet the needs of particular organisations , and have also erected some buildings as a speculative venture . despite some misgivings , these have readily let on satisfactory terms , including in many cases a break clause in the lease allowing for a future increase in rent to reflect rising values in the town . more modest premises are provided on the upper floors over shops in some of the town centres for the small type of office organisation . government departments . government departments with branches established or about to be established in the new towns include her majesty &apos;s stationery office at Basildon , the meteorological office at Bracknell , the Admiralty ( who have a research laboratory at Harlow ) , the general post office and the ministry of transport at Hemel Hempstead and the department of scientific and industrial research at Stevenage . local offices of the ministry of labour , ministry of national insurance and inland revenue are of course established or proposed in all the towns . youth employment . because of the abnormal age structure of the new town populations the number of children reaching school-leaving age , expressed as a percentage of the total population , has been and still is below the national average . but whereas the national annual average will settle down at something like 1.4 per cent after the bulge has passed , in the new towns the percentage will generally go on rising ( in some towns into the middle seventies ) reaching levels of perhaps 2.3 per cent in some towns before it begins to decline . during this period , when large numbers of school-leavers will be looking for jobs , there will be relatively few retirements . for the most part therefore local employment can be provided only by the expansion of existing industry and the introduction of new factories , laboratories and offices , and the expected but not easily stimulated development of the service industries . schemes for training young people in industry and commerce will be particularly important in the new towns . housing requirements of industry . as the Reith committee foresaw , perfect synchronisation of the movement of employing firms with the movement of employed people is not practicable . for short periods over the years some of the London new town corporations have been able to offer a house or a flat at once to anyone eligible for one , but in the main house building has lagged behind the demand . at the present time in most of the towns the waiting period has tended to grow , partly because the buoyancy of industry generates increasing demands , partly because in recent years the pressure on the building industry , the shortage of bricks and other materials , and the shortage of skilled labour , especially in the finishing trades , has made it difficult for corporations to achieve their full programme . it is believed that about 60 per cent of the employees of London firms transferring their business to the new towns moved with them and were thus eligible to rent a corporation house . additional workers are recruited through the industrial selection scheme by arrangement with the ministry of labour . this scheme is designed to ensure that vacancies in the London new towns which can not be filled locally are filled as far as possible from people on London housing lists , who thus become entitled to rent a house in the new town . Londoners not in housing need , but whose departure from London may be assumed to release accommodation there , are recruited for jobs which can not be filled through the industrial selection scheme , and only as a last resort are people from outside London allotted new town houses . as a result , almost 80 per cent of the houses let by the development corporations in the London new towns have gone to Londoners , about half of whom are known to have been on local authority housing lists . tables C , D and E of appendix 16 give details of factories , shops and offices completed and under construction at the end of the year . 