David Cameron was accused tonight of bowing to pressure from lobbyists such as the Tory election strategist Lynton Crosby over a decision to give tax breaks for fracking.
The Government today announced it would cut the taxes paid by fracking companies on their profits to less than half the levy faced by gas and oil producers.
The Independent this week detailed the work that Mr Crosby's lobbying firm, Crosby Textor, does on behalf of companies promoting the controversial method of extracting shale gas.
Mr Cameron has insisted he has never been "lobbied" by his Australian adviser on any policy issue, although he has stopped short of denying they have discussed such subjects.
He has faced repeated calls to explain Mr Crosby's links to the drinks and tobacco industries following the Government decisions to abandon plans for minimum alcohol pricing and plain packaging for cigarettes.
Labour tonight added fracking to the list following the announcement of the low tax regime to be faced by shale extraction companies.
Jon Trickett, the shadow Cabinet Office minister, said: "David Cameron's failure to come clean over his relationship with Lynton Crosby has created a situation where his decisions are open to question.
"Whether it is tobacco or alcohol and now fracking, we need to know what role lobbying has played in deciding what our Prime Minister does."
Crosby Textor represents the Australian Petroleum Production and Exploration Association, which campaigns for fracking. Its members include Dart Energy, a company which holds permits for sites in Scotland.
It also says it holds a "substantial acreage position" in the Bowland Shale under Lancashire and Yorkshire, which is thought to be the world's largest shale gas field.
A spokesman for the campaign group Frack Off said: "Crosby's links with the fracking industry shouldn't come as a surprise to anyone. Corporations have and always will lobby governments.
"You cannot see where government stops and the corporate interests begin. When it comes to an issue like fracking, where human health and our shared environment is being put at risk, we have to question whether those in power are even capable of putting the interests of the general public first."
Mr Cameron has in recent days betrayed his irritation with the continuing focus by the media on his election strategist's business interests and has claimed Labour is stoking up the subject as a distraction from its own problems with trade union influence.
Asked about Mr Crosby, the Prime Minister told Channel 4: "I have been very careful about what I have said which is to say he hasn't lobbied me on any of these issues."
It was reported yesterday that Mr Crosby is expected to become a full-time Conservative adviser in January and stop acting for other clients. He would then focus entirely on Tory election strategy running up to the general election in May 2015, according to senior party sources.
The move would help relieve pressure facing Mr Crosby and his employers over potential conflicts of interests. But critics will argue that he should put his other commercial clients on hold immediately.