Former Home Secretary David Blunkett has urged Welsh assembly member Peter Law to drop out of the race to become MP in a Labour stronghold.
Labour and Conservative supporters greet David Blunkett in Tredegar
Mr Blunkett said Mr Law had "made his point" by leaving Labour to fight in Blaenau Gwent as an independent.
Elsewhere, ex-Tory leader William Hague was in target seats in north Wales.
The Lib Dems focused on opposition to tuition fees and Plaid Cymru suspended electioneering due to former party president Gwynfor Evans' funeral.
An opinion poll also suggested Labour could retain the Conservative target seat of Cardiff North.
The poll, conducted by NOP for ITV Wales, put Labour on 40%, Tories on 35% Lib Dems 19% and Plaid Cymru 5%.
NOP asked 1,005 people by telephone between 21-24 April. Some 31% of those said they were undecided and 13% declined to respond.
Labour had a 14% majority in the 2001 election, and this poll suggests a 4% swing to the Tories in Cardiff North.
Elsewhere, Mr Blunkett, in Tredegar to support Labour candidate Maggie Jones, said the shortage of women in Parliament from Wales had to be addressed.
Mr Law, who left Labour to stand as an independent in his assembly constituency, has protested at the party leadership's decision to impose an all-women shortlist on Blaenau Gwent.
Mr Blunkett said: "I would simply say to the individual who has decided to defect, 'Ok, you've made your point, we know that people think you're a popular figure.
Labour and Tory voices competing with each other for attention
'No imposition from London'
"Stand by, stand out of this and allow us to have an official Labour voice speaking to a Labour government, getting the kind of response that I've heard this afternoon in terms of getting the investment that's needed in this area.'"
Mr Blunkett said it would be "foolish to pretend that there isn't a problem" in the constituency.
But he said a decision on women-only shortlists was taken by Labour some 10 years ago and locally, two years ago. He said there had been "no imposition from London".
Other candidates in Blaenau Gwent are Phillip Lee, Conservative; Peter Osborne, UK Independence Party; John Price, Plaid Cymru and Brian Thomas, Liberal Democrat
At the same time Mr Hague was pounding the pavements of north Wales.
Mr Hague, now a backbencher, stepped down as Tory leader after the last general election, but his first big job in politics was as Welsh secretary from 1995-97 in John Major's government.
The MP for Richmond in Yorkshire was making his second high-profile visit of the campaign to Wales, after visiting a string of seats from south-west to south-east two weeks ago.
Mr Hague, who visited Conwy and Clwyd West, urged his successor Michael Howard to stick to his strategy between now and polling day and predicted the Conservatives would build on the assembly elections by winning Welsh seats.
George Alagiah and Sophie Raworth on the BBC election bus
In Cardiff, the Liberal Democrats staged a mock graduation ceremony to highlight their pledge to scrap tuition and top-up fees.
Students were given "graduation certificates" showing how much debt they will have built up during their time in university.
Lib Dems also promised to expand assembly learning grants they helped to introduce when they were in coalition with Labour in the assembly government.
The BBC election bus, which is touring the UK, visited Cardiff and a series of programmes were broadcast from it during Wednesday.