The snapshot poll shows 36 per cent are planning to vote for Clegg's Labour opponent Oliver Coppard, two points ahead of those who said they would support the deputy prime minister.
All eight of the seats in Ashcroft's poll of marginal constituencies are in Lib Dem battlegrounds, with both Conservatives and Labour hoping to capitalise on the former's abysmal ratings.
This means they are among the most bitterly contested areas in the whole General Election, and are expected to decide which party forms the next government.
In all seats where Lib Dems face Tories the Conservatives have gained support. Clegg's party would hold four of the seats polled, lose three to the Conservatives and one to Labour.
On the national level, the BBC's poll of poll suggests the Tories have managed to close the gap with Labour, the two parties polling neck and neck on 34 per cent. Ukip is on 13 per cent and the Lib Dems are trailing on eight per cent.
The last time Lord Aschroft polled Lib Dem seats was in November.
Today's poll suggests Conservative advances on the national stage are not being reflected in many of the key battleground seats. Only one of the eight seats surveyed, Worcester, showed a Labour lead reversing to a Tory one.
In Croydon Central Labour's lead has dropped from six points to four. Southampton has swung from a tie to an eight-point Labour lead. In all the other seats, Labour has increased its poll lead.