Labour has selected another candidate backed by trade union Unite in a key West Midlands marginal seat.

Former nurse Pete Lowe has been chosen as the candidate in Stourbridge, in the Black Country, where Conservatives have a majority of 5,164.

He was one of 41 potential Labour candidates backed by Unite as part of a campaign to push the party to the left.

Unite-backed candidates have already been selected in Wolverhampton South West, North Warwickshire and Halesowen & Rowley Regis.

Defending the union’s actions over the weekend, Unite General Secretary Len McCluskey said: “Unite is supporting candidates who want radical policies.”

He added: “I make no apologies for that. Unite is proud that it is trying to reclaim Labour from the people that bought in to the free-market myth wholesale, who bet the country’s future on the City of London – and who sometimes fiddled their expenses while they were at it.”

But revelations about Unite’s attempts to influence candidate selection have caused a crisis for Labour leader Ed Miliband.

John Reid, the former Labour Home Secretary, warned that an “ideological battle” over the future of the party is being waged.

And Mr Miliband is expected to use a major speech to announce reforms to the way the party is organised - including caps on spending in candidate selections and elections to senior party positions.

He has already scrapped a Blair-era scheme under which unions were able to pay the subs of new members which they recruited to the party.

Unite’s role is in the spotlight following claims the union attempted to stuff the Falkirk party with union members to ensure the success of its favoured candidate, Karie Murphy, an assistant in Black Country MP Tom Watson’s office.

Mr Watson (Lab West Bromwich East) resigned as Labour’s campaign co-ordinator, although he was not involved in the selection contest.

Police are now investigating the Falkirk selection at the request of the Labour Party.

But Conservatives have demanded Labour suspend the selection process in every constituency where Unite is backing potential candidates.

Coun Alan Taylor, Chairman of the Halesowen and Rowley Regis Conservative Association, said: “Every day there are more and more revelations that raise questions about Labour’s selection here.

“People in Halesowen & Rowley Regis will only get the answers they deserve if Ed Miliband does the right thing and launches a full, transparent and open inquiry.”

Meanwhile, Mr Watson has endorsed Douglas Alexander, the Shadow Foreign Secretary, to replace him as Labour’s campaign co-ordinator.

He said: “Douglas is our most experienced front line strategist. He has worked for both Tony Blair and Gordon Brown and is the natural choice to take forward Labour’s positive message to rebuild our country after the 2015 election.

“It’s obviously not my choice who Ed chooses replace him but if it was Douglas, he would have my full support.

“There are millions of people wanting Labour to win the next general election. A unified labour party is an essential component of our plan.

“I want party members on the ground to be in no doubt that in Westminster, we are completely unified in our desire to win for them in the Euro elections in 2014 and the general election in 2015.

“Douglas, with his characteristic humility and razor sharp mind can refocus the campaign on the issues that matter to people facing a huge fall in living standards”