Liam Byrne's new ministerial post is one job too far, critics claimed last night, warning the West Midlands could come a poor third to his other roles.

As reported in The Birmingham Post yesterday, the Hodge Hill MP has now been appointed as a Treasury Minister, as part of a reshuffle following the resignation of Cabinet Minister Peter Hain. He also continues as a senior Minister responsible for immigration in the Home Office, as well as the official champion of the West Midlands.

The promotion is a vote of confidence in Mr Byrne, seen at Westminster as a high-flying young Minister. However, the move has been strongly criticised by opposition MPs, who said he would find it impossible to give all three roles the time they desperately needed.

Peter Luff, Conservative MP for Mid-Worcestershire, said the Prime Minister was "wrong" to effectively hand Mr Byrne "a fourth job". "Liam Byrne is an MP for Birmingham, is the Home Office Minister for immigration, and then there's his role as West Midlands Minister, which the Government attaches great importance to. Now he's been handed a fourth job.

"The question is what's going to give? Will it be his constituents who see him less, or the West Midlands job? I hope it's not the immigration job, it's a real mess at the moment and that should be his main priority."

Downing Street said the Treasury position would give Mr Byrne greater powers to oversee the reform of Britain 's immigration system. But it comes just a week after Conservative MPs claimed even two jobs were two many for one person to do successfully.

In a Commons debate last week, opposition MPs from across the region complained that he was unable to dedicate enough time to being Minister for the West Midlands.

Mr Byrne has denied the claim, saying that he has travelled the region to meet local councillors and officials, and was busy helping to ensure the refurbishment of Birmingham's New Street station went ahead.

He said the expanded role would mean he now has an office in the Treasury and a larger team of civil servants, giving him more clout in his West Midlands role.

Tory Andrew Mitchell (Con Sutton Coldfield) said: "While it is true that Liam is one of the abler Ministers in this Government, we have been complaining that he is having difficulty doing two jobs. "It is hard to see how this problem will be eased by him being given yet another one."

Mr Byrne said: "It is a big opportunity. It gives me a much bigger team to do the job, so if anything it makes the job easier. It is good news for the West Midlands to have a Minister with a hotline to the Chancellor.

Mr Byrne will be in charge of the UK Borders Agency, which begins work on April 1, and takes over responsibility for Customs at British borders and the UK visas operation, which is currently part of the foreign office.

In other changes, Black Country MP Tom Watson (Lab West Bromwich West) moves from being a party whip to become a Minister in the Cabinet Office, which coordinates policies across Government departments.

The changes follow the resignation of Peter Hain, the former Work and Pensions Secretary and Welsh Secretary, after the election watchdog asked police to investigate his finances.

The Electoral Commission has referred an inquiry over donations to his deputy leadership campaign to Scotland Yard and police are launching an investigation.

Mr Hain's campaign was left with massive debts following his bid to replace John Prescott as his party's deputy leader, which it tried to clear by seeking donations from wealthy individuals.

He declared 17 of these donations - totalling £103,000 - more than four months after the contest ended, placing him in potential breach of electoral law.