Andrew Grice: Bad case of jitters on Tory bandwagon provides a test of nerve for Cameron

Four years after David Cameron became Conservative leader, his party is having an outbreak of the jitters. Senior Tories are not yet in a panic about those opinion polls showing their lead slipping into single figures. But they are, naturally, wondering why it is happening.

On the surface, the Cameron show goes on and it is an impressive one. Yet behind the scenes, all is not well. A Tory mole tells me that Mr Cameron has received about 4,000 letters of protest over dropping his "cast-iron guarantee" that a Tory government would hold a referendum on the EU's Treaty of Lisbon. At one point they were running at 300 a day. The only other time he had such a mountain was after the death of his son Ivan.

The letters were not, it seems, an orchestrated plot by Tory Eurosceptics or the UK Independence Party. The issue for many correspondents was not Europe but trust, a promise broken. I suspect we won't hear Mr Cameron use the phrase "cast-iron guarantee" again.

Trust matters. It is no use offering change if the voters don't believe you will implement it. Trust in politicians generally seems to be at an all-time low. The latest episode in the MPs' expenses saga will hardly help. Perhaps the reason Mr Cameron has never reached the pre-1997 heights to which Tony Blair soared in the polls is that many people who fell for him then felt let down later. Once bitten, twice shy.

You can sense a frustration among the Cameroons. Polls which show the Tories maintaining a lead of 10 points or more are virtually ignored, while those pointing to a hung parliament make waves. Newspapers which proclaimed Mr Cameron had sealed the deal have reverted to asking "can he seal the deal?"

What's gone wrong? Labour and Liberal Democrat strategists think the change in the wind has been created largely by the Tories themselves. Labour's internal polling detected "vulnerabilities" after George Osborne's bold move to spell out some spending cuts at the Tory conference in October. Alistair Darling's reluctance to provide much detail of Labour's inevitable cuts in this week's pre-Budget report makes the Shadow Chancellor look even more brave. But it seems that voters do not like the Osborne medicine, such as the pay freeze for public sector workers earning more than £18,000 a year.

The Liberal Democrats sniffed a change in the air this summer. Their focus groups found that people saw Mr Cameron as dynamic and brave but he scored less well on trust and understanding the lives of ordinary people than he used to. Nick Clegg suspects that, if an election were held now, his party would gain from the Tories as many seats as it lost to them, while his goal of seizing some of Labour's northern heartlands may not be as easy to achieve as it looked six months ago.

Any doubts in voters' minds that Mr Cameron is not "one of us" might well have been reinforced by recent headlines about Zac Goldsmith, Lord Ashcroft, Tory plans to cut inheritance tax and the latest offensive by Labour's class warriors.

There is some frustration in the Shadow Cabinet too. Some members argue that the Tories need to show the voters they are not a one-man band, yet the Cameron circle argues the only way to grab media attention for a speech or policy announcement is for "David or George [Osborne] to do it". A team approach was tried ahead of the Copenhagen summit with a series of speeches on climate change by seven shadow ministers. They were excited at the prospect. But only Mr Osborne got any coverage; the rest were ignored.

The environment, once a winner for Mr Cameron as he hugged a husky, is now more problematic. The Tories know that Mr Brown will be at the centre of events as the Copenhagen talks come to a head next week. It is a reminder that, however weak a government, it can still "do" while oppositions can only talk.

Despite that, the Tories have said nothing about the damaging leaked emails sent by scientists at the University of East Anglia. Plans for Tory frontbenchers to call for an inquiry fizzled out. Mr Cameron did not want to be accused of siding with the climate change sceptics, many of whom are in his own party.

So his boldness has its limits. Allies emphatically deny that he is reluctant to ditch policies on inheritance tax and rewarding marriage in the tax system for fear of upsetting Tory traditionalists. They may well be right, but the image persists of a man who has not yet emulated Mr Blair in taking on his own party to illustrate that it has changed. When he was gliding to victory, perhaps Mr Cameron didn't need to pick a fight with his own side, and risk disunity. But as the Tories' poll lead narrows, some Cameroons believe he needs to remind the public all over again that his party has changed.

That Mr Cameron has had so few wobbles in the past four years is a tribute to his success. There was bound to be an outbreak of pre-election jitters at some point. The Tory leader has steel. He is going to need it now and, more importantly, to show it.