UKIP MEP's switch to the Tories is a blow to Farage's party

Marta Andreasen with UKIP leader Nigel Farage as she is elected an MPE in 2009. Credit: Dominic Lipinski/PA Wire

"Our party is the only one on the up," the UKIP leader Nigel Farage told our cameras in Eastleigh today.

And yet by the end of the day, UKIP was absorbing the news that one of its most prominent MEPs had defected to the Conservatives.

Marta Andreasen is not a name well known to those outside Westminster or Brussels. But if you were to name a UKIP member other than Mr Farage - she might be the one you would choose.

It reinforces UKIP's main problem: that the party is nothing without Nigel Farage.

Report on the Eastleigh by-election, which takes place next week:

He even acknowledged the criticism that UKIP is a "one man party" during our interview today.

That one of his 12 MEPs is joining the Conservatives is a significant blow.

Ms Andreasen cites as one of her reasons for leaving UKIP the decision by her leader not to stand as a candidate in the Eastleigh by-election.

She says that it means UKIP is "only interested in being a pressure group."

And, in what will be music to the ears of many Conservatives, Marta Andreasen says that the Prime Minister's recent speech on Europe, in which he promised a referendum, was a "game changer."

I don't expect too many UKIP supporters in Eastleigh will be persuaded to follow Ms Andreasen's lead but it will be a boost for David Cameron as he defends himself from critics in his own party who argue too many grassroots supporters are leaving the Conservatives for UKIP.

What will be more important for Nigel Farage though, is getting a good result in Eastleigh next Thursday.

For a full list of Eastleigh's by-election candidates, click here.