Boris Johnson snubs Cameron's five invitations to Chequers (and aspirational voters aren't keen either) Polls show that he is far more popular choice than Mr Cameron to occupy No 10. Mr Johnson has also clashed with his fellow Conservative over the building of a third runway at Heathrow, which the Mayor vehemently opposes but which the Government has put back on the agenda. The most recent snubbed invitation is understood to have occurred last weekend, when Mr and Mrs Johnson and their children visited the Prime Minister and his wife, Samantha, at Chequers but declined to stay overnight. Rather than dine at the Buckinghamshire estate, the two families visited a nearby pub for lunch. A Downing Street source denied that there were serious tensions between the two men, saying: "David and Boris are actually quite close. Boris has a busy diary too, and the PM understands that. While he is less popular than Mr Johnson, new opinion poll by TNS-BMRB has found that while Mr Cameron remains the most popular of the three main party leaders to be prime minister. Among uncommitted voters he enjoys an 11 per cent lead over Ed Miliband, with 42 per cent saying they have confidence in Mr Cameron compared to 31 per cent for the Labour leader. However, his lead is slipping among the broader electorate. Overall, the poll found that the Conservatives now have the lowest level of support since the last general election, with just 28 per cent of the vote compared to 44 per cent for Labour. The survey comes as private polling by Lord Ashcroft, the former party donor, finds that the Conservatives have lost the support of the key aspiring working class section of the electorate. So-called C2 blue collar workers, who make up as much as 15 per cent of voters and who propelled Baroness Thatcher to a series of election victories in the 1980s, are now more likely to vote Labour. Polling by multi-millionaire Lord Ashcroft found that the group the favoured the Conservatives at the last general election, with the party winning 29 per cent of these voters compared to 19 per cent for Labour, but now backed Mr Miliband's party by 25 per cent to 20 per cent for the Tories. However, this group also thought that Mr Cameron made a stronger prime minister than Mr Miliband. With the Conservatives preparing to gather for their annual conference in Birmingham next week, Lord Ashcroft said that wooing back the C2s would be vital if the party wanted to win the next election, expected in 2015. He told the Daily Mail: "There has been a substantial swing to Labour from both the Conservatives and Lib Dems in this section, which the Tories won comfortably at the 2010 election." Further polling of the group, nicknamed "suspicious strivers" found that they tended to think people expect too much from government, opposed penalising top earners with high taxes and feared that expanding employment rights could hamper the creation of new jobs. They were concerned that hard work was less important than personal connections when it came to getting on in life, thought that they paid the most taxes while receiving the least in return, and were worried that their children would not get into university, find good jobs, or be able to afford a house in future. In more bad news for the Prime Minister, a separate poll by YouGov for The Sun found that the creature most associated with Mr Cameron in the minds of voters was a snake. A third complained that he had not lived up to their expectations, more than half said that they did not know what he stood for and just 13 per cent thought that he had done a good job so far. Nearly nine out of 10 of those who responded to the poll said that Mr Cameron and the Conservative Party represented the rich, with only 14 per cent saying that he was close to working class people. Asked which animal the Prime Minister most reminded them of, 20 per cent said a snake, 15 per cent a Labrador dog and eight per cent a poodle.