Mr Law became ill shortly before the 2005 election

There were reports party members had contacted some voters in the south Wales constituency after Mr Law's death from a brain tumour last Tuesday.

The party said members were carrying out a survey across Wales, which had now been suspended in Blaenau Gwent.

Canvassing would not begin until after Mr Law's funeral on Thursday, it added.

On Sunday, Mr Law's widow Trish revealed she was considering standing in one of the two vacant seats.

The Labour Party does respect the enormous contribution which Peter Law made to public life Wayne David MP

Caerphilly MP Wayne David told BBC Wales any contact with voters was "clearly a mistake" but added an apology was needed if that had been the case.

He said: "There might have been one or two individuals who telephoned from outside Wales canvassing in different parts of the country and might have happened to have telephoned people in Blaenau Gwent.

"If that was the case, there needs to be an apology.

"It was clearly a mistake, as the Labour Party does respect the enormous contribution which Peter Law made to public life and we intend to honour that until after his funeral."

Mr Law, who was a serving Labour AM, stood as an Independent MP - and defeated the Labour Party - in protest at all-women shortlists to replace the retiring MP, Llew Smith, in 2005.

He was diagnosed with a brain tumour shortly before the election, but following treatment decided to remain in the contest and overturned a 19,000 majority.

He died on Tuesday aged 58. His funeral will take place on Thursday in Ebbw Vale.