A row has broken out over the defection of a Welsh Conservative to Labour.
David Anstee has left the Conservatives for Labour
Labour quoted Prime Minister Gordon Brown welcoming the decision by Rhondda activist David Anstee, 26.
But the Tories dismissed Labour's claim that Mr Anstee helped put together the Conservative Welsh assembly manifesto as outrageous and untruthful.
Conservatives said he was "in no way involved" with the manifesto and said it would refer the matter to the commissioner for standards.
"Although I regret that David Anstee has decided to leave, his position in the party has been massively overstated," said a Conservative spokesperson.
"He played no role in the production of our recent highly successful manifesto for the assembly elections."
The Tories said they would refer it to the commissioner for standards, unless there was a "full apology" from Rhondda AM Leighton Andrews, who they identified as the man behind the press release.
In response, a Welsh Labour spokesperson said Mr Anstee had attended "a meeting of the Welsh Conservative policy forum, run by Tory policy co-ordinator David Melding AM, to discuss policies for the 2007 election".
But the Tories said the fact Mr Anstee claimed to have attended a policy forum did not mean he had played a role in writing the manifesto.
In its initial press release, Labour said Mr Anstee was a 26-year-old school teacher who had been vice-chairman of the Rhondda Conservatives.
Mr Andrews, who is deputy minister for regeneration in the Welsh Assembly Government, said the defection would "prove to be another blow to the leadership of David Cameron in London and Nick Bourne in Cardiff".
"David Anstee is precisely the kind of talent they want to attract to their party, but he sees the future of Britain as being best served by the Labour Party," he said.
Mr Anstee said he had been "really impressed by Gordon Brown's leadership".
"His strength and vision for Britain has been inspiring," he said.
"We need a serious leader for serious times, to meet the challenges of security, global warming and housing."
The prime minister said he was pleased that Mr Anstee had "listened to my call for moderate Conservatives to join the Labour party and help build a better Britain".
"I welcome him to the party and look forward to hearing of his positive contribution in the future."