Voters will go to the polls in Blaenau Gwent in four weeks to decide their new MP and Welsh assembly member.
The by-elections are being held after the death of Peter Law
The by-election is being held after the death of Peter Law, who was the independent MP and AM.
An opinion poll by NOP for ITV Wales has suggested that Labour candidate Owen Smith is ahead of his rivals for the parliamentary seat.
It also suggested that the independent candidate Trish Law, Mr Law's widow, is leading the assembly race.
In the Westminster election, the poll put Mr Smith on 47%, ahead of Mr Law's former agent, independent Dai Davies, on 35%.
The survey suggested that support for the three other candidates - Conservative, Liberal Democrat and Plaid Cymru - was in single figures.
NOP OPINION POLL
Owen Smith (Lab): 47%
Dai Davies (ind): 35%
Amy Kitcher (Lib Dem): 6%
Steffan Lewis (Plaid): 6%
Margrit Williams (Con) 5%
Trish Law (ind): 43%
John Hopkins (Lab): 40%
Stephen Bard (Lib Dem) 6%
John Price (Plaid):6%
Jon Burns (Con): 3%
John Matthews (Green): 2%
NOP interviewed a representative sample of 1,000 adults by phone between 24 - 28 May
In the race for the assembly seat, the poll suggested that Mrs Law is supported by 43%, with Labour candidate on John Hopkins on 40%. The other four candidates were - Conservative, Lib Dem, Plaid and Green - were put in single figures.
Voting intention was based on all those certain or very likely to vote and who named a candidate they intend or are likely to vote for.
Mr Law died in April aged 58 after a brain tumour.
He left Labour over the imposition of all-women candidates' shortlists and won Blaenau Gwent as an independent at the last general election, overturning a 19,000 Labour majority.
He took the seat, once represented by Aneurin Bevan and Michael Foot, with a majority of more than 9,000.
At the time of the elections last May, he was already the constituency's AM.
His defection meant Labour lost its overall working majority in the Welsh assembly.