With David Cameron increasingly likely to win the next election, many public affairs agencies are desperate to sign up a top Tory to impress potential clients.

Labour's crushing defeat in last week's Crewe and Nantwich by-election is the latest development to push up the value of Tory advisers.

One public affairs agency head said: 'There are a small number of people close to Cameron and Osborne, and everyone wants a piece of them. We are talking here about senior heavyweight figures - not ex-parliamentary aides who once worked for some backbench MP. But these people are now asking for £20,0000 or £30,000 more than what they would have been worth at Christmas. They have effectively added over £20,000 to their value over the past few months.'

Bell Pottinger Public Affairs chairman Peter Bingle agreed that Tory candidates were commanding much bigger salaries than a few months ago, but said the best aides were unlikely to leave with Cameron so close to power. He said: 'Anybody who's any good will want to stay advising Cameron and make a move in two years' time, when they will be worth much more.'

Bingle suggested that with members of Cameron's inner circle unlikely to leave, many agencies would end up bringing in low-level Tory aides on inflated salaries. 'Teaboys are going to be appointed as senior advisers,' he warned.