THE Chancellor will introduce legislation this week aimed at prising £40 billion in investment from the private sector for infrastructure, to answer critics of his handling of the economy.

The fresh injection of private finance into UK infrastructure was signalled in July, with a pledge to bring in the necessary legislation as soon as possible. It will be introduced within the first week of MPs' return to Westminster and fast-tracked on to the Statute Book within two months.

More will be announced later in the week about a related £10bn boost to housing construction, while the other main projects involved could cover utilities, transport, health, education or even courts and prisons.

The Infrastructure (Financial Assistance) Bill will create a new power "to incur expenditure on the provision of guarantees" on infrastructure, and will impact on the whole UK, perhaps offering a mechanism for the Scottish Government's call for capital investment.

There has been a flurry of criticism of Coalition leaders from within both parties, which has been fierce even by the standards normally generated by re-shuffle fever.

This prompted Prime Minister David Cameron and his Chancellor, George Osborne, to come out fighting over the weekend, while Deputy Prime Minister Nick Clegg was no less under siege within the Liberal Democrats.

There will be another piece of legislation this week in the form of an Economy Bill designed to ease red tape and speed up the planning process, but this will mainly affect England.

First Minister Alex Salmond, who returns to Holyrood this week, was critical of the time the UK Government has taken to come forward with an infrastructure announcement.

He said: "It seems that it takes an insult from his back-benches to stir the Prime Minister into action, whilst it has been blatantly obvious, for six months or more, that action on capital investment is needed.

"The Scottish Government submitted a list of shovel-ready projects to the UK Government in February, following a request from the Prime Minister, but no action has yet been taken by the Prime Minister or his Chancellor. The Scottish Government has consistently argued for capital investment to boost not just construction, but also the wider economy.

"Ongoing dither, delay, division and disarray from the Coalition Government will cost Scotland dear."

Both Mr Cameron and Mr Osborne made repeated references to the Olympics and Paralympics as demonstrating that Britain can compete in the world and demonstrate success, using this as an argument against the snail-like pace of the planning laws south of the Border.

The Prime Minister said: "The nations we're competing against don't stand for this kind of paralysis and neither must we. Frankly, I am frustrated by the hoops you have to jump through to get anything done – and I come back to Parliament more determined than ever to cut through the dither."

Mr Osborne, under fire from Tory backbencher Brian Binley and others who think he should concentrate either on his Treasury work or his party strategy job, said: "Of course, I read all these people coming up with different proposals for what we should do. Quite often they are mutually contradictory.

"I would say this to all the critics, on the Labour side and indeed even in the Coalition: Get behind the Government in making it easier to develop things, to get things built, to support infrastructure development. That is deregulation."

Some in the LibDems, such as Lord Oakeshott and veteran backbencher Adrian Sanders, have also been turning on Mr Clegg, to the point that Business Secretary Vince Cable, who many would prefer as leader, had to come to his support.

"I don't give any time to these personal criticisms of Nick Clegg which are being made at the moment," he said. "It is inevitable in the mid-term of parliament when party popularities wane, when difficult decisions are being made."