Figures show that the inquiry into Birmingham-based MG Rover has cost the Government £15 million since the firm collapsed in April 2005.
The investigation under the Companies Act began after the car maker collapsed, which led to 6,000 job losses, and is an attempt to establish what went wrong between Phoenix Venture's acquisition of the firm in 2000 and administrators being brought in.
However, the probe has been running for more than four years and so far no end date has been set.
In a written parliamentary answer to Peter Luff, Tory chairman of the Commons Business and Enterprise Select Committee, business minister Pat McFadden gave updates on the progress.
He revealed that costs as of March 31 were £12,502,416, with £447,406 in "disbursements" and a VAT bill of £2,241,554.
Mr McFadden said: "As is normal in Companies Act inspections, the inspectors were not given a specific target date for the completion of their investigation, nor are they working to a pre-determined financial ceiling.
"Either might restrict the depth and thoroughness of their inquiry."
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