 It is, you will have read, the 25th anniversary of the privatisation of British Gas. all three successor companies have been in the news of late, and all three neatly indicate the virtues and dangers of diversifying off your original patch.  First, a bit of context. The old state utilities were mainly privatised with the original board intact, though the odd finance director was drafted in from the City to give a bit of financial nous.  This threw on to the public stage some civil servants who could hold their own with the very best in British boardrooms.  One thinks of Sir Denis Rooke, the former British Gas chairman, who died in 2008, a man never afraid to take on Whitehall in defence of the industry he loved.  But in many cases, and I will name no names, the head of the local water or power utility found himself, and I use the pronoun deliberately, the chief executive of a publicly quoted company. For some, it rather went to their heads.  They were easy meat for money-grubbing investment bankers advising them to do deals outside their range of competence. Several could probably have been persuaded of the synergies available from buying a chain of sweetshops, should said investment banker happen to have one such for sale.  United Utilities, for example, was created by the merger of North West Water and Norweb, the regional electricity distributor, in 1995. It bougth a New Jersey water company. It went to work in Malaysia, Mexico City and Sidney.  The company had a telecoms business. It bought into australia, the Philippines, even Estonia. Not all were a disaster.  But over the past few years United has been retreating back into its core business, a local water company, which is what it is today. I have suggested, with a degree of seriousness, that the company is so tight these days it will not even pay for a change of name back to North West Water.  There were any number of such deals done. Some were more successful. National Grid, into which was merged Lattice, British Gas's daftly named pipelines network, in 2002, has built a power distribution business in the US which is now equal in size to the UK and serves about seven million customers in the north eastern seaboard.  This allowed it to escape from the heavily regulated UK market. The experience has not entirely been a happy one. The US market, where it serves, is if anything even more regulated. The earnings are subject to peaks and troughs. On balance, though, the decision to escape the shackles of the UK has been positive.  International Power was created by the demerger of National Power, once part of the old Central Electricity Generating board, in 2000 with the specific intention of creating a vehicle that would highlight the company's diversification overseas and the growth prospects there.  It is now 70 per cent owned by GDF Suez of France and has ambitious plans to spend ?4 billion a year building more energy projects around the world in high growth markets such as Latin america, the Middle East and asia. The demerger must be judged a success; the shares are up by more than 50 per cent since they first listed in October 2000.  Sometimes demergers do work. One of the reasons for breaking up British Gas into Centrica and BG Group was to emphasise the attractions of the latter. The  