Lord Ashcroft has published his survey of the state of the parties in 17 Liberal Democrat-Conservative marginals.

While the overall trend is for a swing from the Lib Dems to the Tories of 3.5%, there is a wide variation from seat to seat. The survey suggests there might not be a uniform shift of opinion away from the Lib Dems. In fact, in three polls, the swing is actually from the Tories to the Lib Dems.

This shouldn’t be that surprising. I wondered last month whether Paul Burstow in Sutton and Cheam might defy the national trend and hang on to his seat. Sure enough, he is one of a trio of Lib Dems in marginal constituencies that Ashcroft thinks may survive – despite having a majority of just 1,608.

The other two are Mark Hunter in Cheadle (majority: 3,272) and Mike Thornton in Eastleigh, who held the seat for the Lib Dems in a by-election in 2013. Thornton’s 1,771 majority is over Ukip, but only around 3,000 votes separate him from the Tories.

In all three cases, I’m guessing the sitting MP has a strong local following and/or the Tory challenge is not very well established.

Seven seats in Lord Ashcroft’s survey would switch from Lib Dem to Tory were an election held tomorrow. They are Solihull, Dorset Mid & Poole North, Wells, St Austell & Newquay, Somerton & Frome, St Ives and Chippenham.

Here’s a reminder of the Lib Dems’ 10 seats most vulnerable to the Conservatives:

Lord Ashcroft’s polls suggest seven of these 10 would fall to the Tories. Sutton and Cheam would remain Lib Dem. Cornwall North would be tied. Ashcroft did not run a poll in the remaining seat of Berwick-upon-Tweed.

When I made my most recent prediction of the general election result, I forecast the Tories to gain only six seats from the Lib Dems. Today’s survey implies that total could be larger, though not by many. The overall swing of 3.5%, if applied uniformly, would lead to Lib Dem losses of over a dozen – but that’s overlooking variations such as the 4.5% swing from Conservative to Lib Dem in Sutton & Cheam.

I’m not sure this survey tells us much more that we hadn’t already guessed. If anything, the damage isn’t quite as severe as the more pessimistic pundits have liked to make out. What could be more significant is the scale of marginal seats the Lib Dems may lose to Labour. Fortunately, this is the subject of Lord Ashcroft’s next set of polls, due some time in July.

Two other points. Lord Ashcroft also ran polls in six Tory marginals where the Lib Dems are close behind in second place. None of them showed a swing to the Lib Dems, not even Camborne & Redruth where sitting Tory MP George Eustice has a majority of just 66.

Finally, a note on the scores polled by Ukip in some of these seats. While the party got 26% in Camborne and Redruth, 25% in St Austell & Newquay and 22% in Truro & Falmouth, nowhere did it come close to being in first place. The impact of Ukip may have contributed to the tie in Cornwall North, but that aside there were no what I would call “persuasive” disruptions to the Tory-Lib Dem dynamic in any of the marginal seats included in the survey.