The official inquiry into MG Rover has cost taxpayers more than £4.5m, the Department of Trade and Industry has revealed. The cost is shooting up by £500,000 every month.
Birmingham MP Richard Burden (Lab Northfield) said: "It is an awful lot of money and this inquiry needs to be completed as soon as possible."
Ministers launched the investigation after the Birmingham carmaker went into administration last April, closing its factory in Longbridge.
The collapse cost 6,000 jobs and followed extensive Government efforts to obtain a rescue deal.
Forensic accountancy firm BDO Stoy Hayward has been paid £4.1 million so far. It is combing through MG Rover's accounts in a bid to discover actually what happened.
The inquiry is led by Gervase MacGregor, the head of the BDO Stoy Hayward team, and barrister Guy Newey QC.
Mr Burden, whose constituency includes the Longbridge plant, said: "I have been interviewed by the inspectors myself, and expressed concern about the cost and amount of time this inquiry is taking.
"But last year there was widespread agreement that we needed a detailed and independent inquiry into what happened to Rover.
"That will inevitably cost money. However, I think we have reached a point where people want the answers."
A DTI spokesman stressed that the payments were made to the firm, "and not Mr MacGregor personally, and related to the time spent by him and others within BDO on the inspection".
The inspectors have not been set any deadline. A DTI spokesman said limiting the length of the inquiry "might restrict the depth and thoroughness of their inquiry".
The Government warned earlier this year that the inquiry, which began last June, would not report before mid-2006 "at the earliest".
Officials said the inspectors were "masters of their own procedures, as far as the investigation is concerned" but were meeting with the DTI regularly to "monitor progress and to ensure that the momentum of the investigation is maintained".
The collapse of Rover is expected to cost taxpayers more than £250 million, a National Audit Office report warned earlier this year.
This includes a £6.5m state loan to allow Rover to keep trading for a week after it went into administration, of which £5.2 million is unlikely ever to be paid back.
Around £146 million is likely to be spent on the support package put in place after the collapse to help the local economy.
A House of Commons inquiry has heard that Ministers wanted to lend Rover £110 million to help it form a joint venture partnership with Chinese motor manufacturer SAIC.
They were talked out of it by civil servants, the Commons Public Accounts Committee was told.