Ofgem is set to publish new figures estimating that energy companies are in line to increase their margins, describing the findings as "clearly cause for concern".

Ofgem chief executive Dermot Nolan told the Energy and Climate Change Committee that he believed the figures due to be published on Thursday would show that a typical large supplier would increase its margins over the next 12 months.

The regulator's supply market indicator - which it describes as a forward-looking view of cost trends for a typical large energy supplier - are likely to be disputed by the industry body Energy UK, which has previously complained that it is "inaccurate", "not reliable" and "being used in a way that is misleading and must be reformed".

Mr Nolan told MPs: "Wholesale prices have fallen dramatically in the last few weeks, as you'll be aware.

"Our supply market indicator is due to be published this Thursday. What it might say, and I don't feel I should give the figure, but I do believe it will show an increasing margin, and that is clearly cause for concern.

"We are trying to get the message out that it is easy to switch and you can gain from switching.

"But there is the major question of whether and how wholesale cuts that have clearly occurred are being passed on. It is something we will continue to monitor and measure.

"One thing I want to do very, very clearly as a regulator is shine as much light into this area as possible, publish as much data, really put firms under the microscope in terms of saying' What have you done, what are the correct margins that are in place?'.

Mr Nolan added: "The whole rocket and feather effect was one of the fundamental reasons we referred the market to the CMA (Competition and Markets Authority).

"In the state of the market report we published last year we found strong evidence that actually said wholesale prices rise and retail prices move quickly but that actually they don't fall in the same way.

"We felt that we didn't just have an opinion or point of view, we had strong statistical evidence.

"If this phenomenon is still going on, and Thursday may make it slightly clearer as to whether or not we believe that lack of responsiveness is still there, then I would see that as an ongoing problem and something that the CMA would be looking at very carefully.

"What they will do with that I don't know but they are due to publish their interim conclusions in June."

In November Ofgem estimated firms would make a £105 profit per household over the year - or 8% of the annual dual fuel bill, around £2 higher than the previous month's estimate due to further reductions in expected wholesale costs over the next six months.

All of the biggest firms with the exception of EDF have recently announced cuts in gas tariffs in response to the falling cost of wholesale energy.

Citizens Advice chief executive Gillian Guy said: " We have now had inadequate price cuts from five out of the Big Six energy firms.

"Consumers need a better offer than 5% price cuts to show that energy firms are really passing on a year of falling wholesale costs. Instead of falling into line EDF should now show up the other firms by giving its customers a price cut to celebrate.

"The CMA investigation must result in a market that leaves all consumers confident they can get value for money on their energy bills. Loyal customers who can often be older or on prepayment meters should not be left out in the cold whilst only the savviest people can switch to get better deals.

"We have found there can be differences of £200 between what firms offer for their standard and their cheapest tariffs."