The defection of a Conservative councillor to Ukip is a "huge blow for David Cameron's authority", Labour has said.
The party's shadow minister without portfolio, Jon Trickett, said the move showed even the Prime Minister's candidates "know he cannot win a majority".
"Ukip and the Tories increasingly share the same people as well as the same policies," he said.
"Both stand for increased health service privatisation, extreme spending plans which threaten the NHS and further tax breaks for those at the top."
“David Cameron will not rule out working with UKIP, but this is clearly what his party wants. David Cameron must now come clean and tell us what his plans are to do a deal with Nigel Farage and UKIP.”
The Conservatives say a parliamentary candidate who "defected" to Ukip had already been sacked.
A spokesman for the Tories dismissed Mike Whitehead's announcement as "cynical, misleading and utterly calculating to try and score political points".
"He refused to support the local Conservative council candidate and so we wrote to him last week to say that his position was untenable and he could not stand for us at the general election.
"We were already selecting a new candidate for this constituency."
The defection of a Conservative parliamentary candidate to Ukip has dealt "another hammer blow to Tory pretensions in the north of England", Nigel Farage has said.
The Ukip leader said he was "delighted" to welcome Mike Whitehead - candidate for Hull West and Hessle - to the party, and said the move was proof "that today the real party of opposition to Labour in the north is Ukip".
A Conservative parliamentary candidate has defected to Ukip, the party has announced.
Mike Whitehead, an East Riding councillor standing for selection as MP for Hull West and Hessle, said he was "disgusted" with the behaviour of the ruling Tory group in East Yorkshire, and the "wilful refusal" of the national Conservative Party to intervene.
He also insisted the "secretive" council needed to be "opened up" and made more transparent".
Whitehead said he had been concerned about the behaviour of the controlling group of Tories since 2011, when seven Conservative councillors from Haltemprice and Howden resigned, claiming bullying and intimidation.
His parliamentary constituency is currently deemed a safe Labour territory, with former home secretary Alan Johnson defending a 5,700 majority from 2010, when the Conservatives finished third.
A helicopter has crashed into the sea near Flamborough, East Yorkshire, Humberside Police said.
The Duke of Cambridge revealed he is a fan of British rockers Coldplay, during a visit to a school in East Yorkshire today.
When William was asked by pupils at Goole High School what music he liked, the Duke was heard to reply: "I really like Coldplay, Linkin Park."
He turned down an offer by pupils who are part of the school's samba band to play one of the drums, telling them: "I used to play the piano, trumpet and drums when I was your age but I couldn't read music.
"There's only so much you can remember from the top of your head."
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Two people have been rescued after abandoning their pleasure boat when it caught fire this morning on the River Ouse in East Yorkshire.
The 36ft Moonraker cruiser was said to be "well alight" by the time the pair were pulled from the water, uninjured, near Blacktoft by Humber Rescue volunteers.
The vessel, which was carrying a gas cylinder and 125 litres of diesel fuel as it drifted upstream near Reedness, later sunk.
Emergency services, who were called out at 8:00am, mobilised a firefighting tug but it was not used.
More than 1,000 explosives from the Second World War have been uncovered following a landslide at a beach. A cordon was put in place after the ordnance at Mappleton beach near Hornsea, East Yorkshire, became exposed. Army bomb disposal experts have been dealing with the incident since yesterday.
Ordnance is uncovered several times a year due to coastal erosion but with the recent poor weather we've had it's exacerbated the erosion and all this has been uncovered. There is a mix of rockets, mortars, 25lb bombs and more... We are advising people to stay away from the area.