John Reid has been appointed as leader of the House of Commons, Downing Street revealed on Friday.

He is in turn replaced as party chairman by Ian McCartney.

The appointment of Dr Reid, a bruising loyalist, is unlikely to go down well with opposition MPs.

Traditionally the post of Commons leader combines doing the government's bidding with representing the interests of MPs.

They fear he will use the role to press the government's case at the expense of the rights of the Commons.

The post has been vacant for three weeks following the resignation of Robin Cook.

His new post is his fourth cabinet job in four years.

Dr Reid, a former Northern Ireland secretary, has been a vocal defender of the prime minister during the Iraq conflict.

He has also been pivotal in pressing the government's case on public service reform to sceptical grassroots members.

McCartney is likely to continue in a similar vein - although he may adopt a less confrontational style.

His appointment to the Cabinet is seen as a reward for the unstinting loyalty he has shown to the leadership.

Popular on the backbenches, the 51-year-old is down to earth and a favourite on the constituency circuit.

His appointment brought a warm welcome from the unions who view him as an ally.

TUC general secretary-elect Brendan Barber said: "Trade unionists everywhere will welcome Ian McCartney's appointment to the Cabinet. His broad understanding of the labour movement and key roles at the heart of government since 1997 gives him unrivalled experience for this job."

Blair is expected to use the new chairman to repair relations damaged by his support for the US-led conflict against Saddam Hussein.

Speaking following his promotion, McCartney said: I'm very much on board with party members who are saying now that they want to make sure in the future that the government is more and more involved with them.

"You can't have an effective long-term government unless you have got an effective campaigning party at a local level."

His promotion opens they way for the appointment of a new minister of state at the Department for Work and Pensions.

MPs had earlier raised concerns at the three week delay in replacing Cook. Earlier this week they expressed bemusement at the delay.

It is thought Blair will delay appointing a successor to McCartney until he conducts a wider reshuffle once the war is over.