The aims of the Government's flagship environmental policy are still unclear after three years in power, an influential group of MPs has warned.

There has been no precise explanation of what the Green Deal is trying to achieve, said Tim Yeo, chairman of the Energy and Climate Change Committee.

Mr Yeo described it as "unacceptable" that ministers are unable to define how the policy would be a success.

The Green Deal was launched by the coalition Government as part of an initiative to help households and businesses improve their energy efficiency.

And although the policy formed a key part of the coalition's pledge to be the "greenest government ever", the Committee said ministers have not outlined any clear expected outcomes.

Mr Yeo said that at a time when improving energy efficiency is a crucial issue given the recent rises in energy bills, his Committee wants the Green Deal to be successful.

However, he indicated that makes it all the more important to carefully scrutinise such a high-profile policy to make sure it is working.

The Committee has therefore set out plans to monitor the progress of the Green Deal in the coming years or, as Mr Yeo put it, "keep a watchful eye" on its progress.

He said: "We will be looking to see how many people are taking up the Green Deal and whether they are seeing genuine savings on their energy bills."

In its report entitled The Green Deal: watching brief, the Committee called on the Government to publish details of the policy's progress and achievements so that any problems can be resolved as early as possible.

The report warned there are several potential challenges that could restrict uptake of the Green Deal, such as difficulties experienced by those in rented accommodation gaining the consent of their landlords to improve their property's energy efficiency.

Another potential stumbling block may be a reluctance on the part of homeowners to have disruptive building work done on their property, the report suggested.

"We will also want to ensure that Green Deal companies are providing a good service to customers to make certain we do not see a repeat of the doorstep selling and mis-selling that energy companies have been engaged in recently," Mr Yeo added.