Nationwide support for Ukip has fallen by 25% over the last six months

Comes after leaked poll showed the Ukip leader on course to lose in Thanet

Nigel Farage suffered a fresh blow today after a poll of key marginal seats revealed voters were deserting Ukip in droves and returning to Labour and the Tories.

In 10 battleground constituencies polled by the Tory peer Lord Ashcroft, Ukip's vote has fallen in nine.

Support for Mr Farage's party has more than halved in two seats and by more than a third in most of the others.

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In 10 battleground constituencies polled by the Tory peer Lord Ashcroft, Ukip's vote has fallen in nine of them

Support for Mr Farage's party has more than halved in two seats and by more than a third in most of the others

The revelation comes after a leaked poll revealed Mr Farage is on course to lose his own Parliamentary election battle in Ukip's heartland in Kent.

The Ukip leader has seen his support in Thanet South collapse from a 12 point lead over the Tories. He is now sitting in second place in the Kent constituency, 1 per cent below his Conservative rival Craig Mackinlay and only just ahead of Labour.

Today's polling also mirrors nationwide polls which show that Ukip's support has fallen by 25 per cent in the last six months alone.

In November last year 18 per cent of voters said they were planning to vote for Ukip – but this has since fallen to less than 12.5 per cent, with polling experts now predicting that it could drop below 10 per cent by next month.

Ukip's dramatic collapse in support has not, however, led to a surge in support for the Tories.

According to Lord Ashcroft's poll of 10 marginal constituencies today, the Tories are set to lose four seats to Labour but cling on in five. A tenth seat is too close to call between the two main Westminster parties.

The four seats Labour are set to gain according to Lord Ashcroft are Harrow East, Hove, Morecambe & Linsdale and Stockton South.

According to Lord Ashcroft's poll of 10 marginal constituencies today, the Tories are set to lose four seats to Labour but cling on to at least five

The results suggest Labour has strengthened its position since Lord Ashcroft polled the same constituencies last year, when the party was only picking up three seats from the Tories.

The one seat which switched since last time is Harrow East in West London where a small Tory lead has turned a four-point advantage for Labour.

But if the General Election was held tomorrow, the Tories would hold on to five of the 10 marginal seats it won in 2010 – Pendle, Blackpool North & Cleveleys, Loughborough, Kingswood and Gloucester.

Comic Al Murray, also known as the Pub Landlord, arrived at Thanet District Council offices in Margate, Kent, today to hand in his nomination papers as he stands in the South Thanet seat against Ukip leader Nigel Farage

With the race in Thanet South going down to the wire, any votes the comic takes from the main candidates could prove costly

Lord Ashcroft has one constituency – Pudsey – where Labour and the Tories are tied.

But the real shift in the seats, according to the Tory peer's polling, is the huge squeeze on Ukip's vote.

Lord Ashcroft said: 'The most notable movement across the board in this round of polling was a move towards the two main parties at the expense of UKIP.

'In this group of ten seats, the UKIP share had fallen significantly – by up to ten points – in nine of the ten seats polled.

'In only one seat did I find the lead had switched between parties – Harrow East, where a three-point Conservative lead in December had become a four-point lead for Labour.'