 aFTER a period in the doldrums, Vince Cable, the Business Secretary, has bounced back to emerge as the Liberal Democrat politician most highly rated by the party's members.  The survey of 550 grassroots activists by the Liberal Democrat Voice website suggests that Mr Cable would be a strong candidate to succeed Nick Clegg if he stands down as the party's leader before the next general election.  It confirms a remarkable comeback by Mr Cable. Liberal Democrat insiders believed that his prospects of leading the party were over last December after he told undercover journalists posing as constituents he had "declared war" on the media magnate Rupert Murdoch over News Corp's bid to raise its stake in BSkyB from 39 to 100 per cent.  The takeover was abandoned this summer in the midst of the phone-hacking scandal at Mr Murdoch's News of the World. Friends believe Mr Cable, who is 68, still has an appetite for the party's top job. Mr Clegg has insisted he will lead it into the next election but there is speculation he may quit in 2014 to become Britain's European Commissioner.  In april, Mr Cable had a net satisfaction rating of 51 per cent among party members, according to Liberal Democrat Voice. That has now jumped to 72 per cent and he has overtaken his two most likely rivals for the leadership.  Chris Huhne, the Energy Secretary, has seen his net satisfaction rating drop from 63 to 53 per cent in the past six months. He has been the subject of a police investigation over allegations, which he strongly denies, that he asked his former wife to take points on her driving licence for a speeding offence he committed.  Tim Farron, the Liberal Democrat president, could emerge as Mr Cable's main rival. He has a net satisfaction rating of 70 per cent and is seen by many party insiders as Mr Clegg's most likely successor. While he lacks ministerial experience, being outside the Government could prove an advantage if the Coalition  