Tories deny key adviser Andrew Cooper set to quit in bid to fend off 'nasty party' tag

Downing Streeet struggled to fend off speculation yesterday that David Cameron is on the point of losing another of the advisers who helped him steer the Conservative Party away from its "nasty party" image.

Andrew Cooper, Mr Cameron's pollster, who has spent more than 15 years trying to impress on the Conservative Party the need to adapt and modernise, is said to be leaving because of professional disagreements with the Tories' Australian-born election strategist, Lynton Crosby.

Downing Street issued a formal denial of a story in the Mail on Sunday that Mr Cooper was going back to Populus, the private polling company he co-founded, but without any further comment or explanation. Mr Cooper is a controversial figure in Tory circles, because of his role in persuading David Cameron to legalise gay marriage.

If Mr Cooper does leave, he won't be the first "modernising" Downing Street adviser to quit No 10. Others include Steve Hilton, Cameron's director of strategy, in March 2012, Sean Worth, Cameron's adviser on public service reform, in June 2012, James O'Shaughnessy, head of policy, in October 2011, Tim Chatwin, head of strategic communications, in September 2011, and technology adviser Rohan Silva in April 2013.