The House of Commons public accounts committee said the corporation underestimated scale and complexity of the E20 project, which will be completed nearly five years late.

The current EastEnders external set was built 35 years ago and is no longer fit for purpose.

The completion of E20 is seen as critical if EastEnders is to compete successfully against rival shows and retain audiences in a context where fewer people are watching traditional linear TV.

However, MPs said E20 is late and over budget due to the BBC’s fundamental project management failures.

The committee said it is concerned that E20 has gone off-track yet again after the 26-month delay in 2016, and is disappointed by the BBC’s complacency in managing this project, particularly in its early stages.

The project is now set to cost licence fee payers £87 million – £27m more than budgeted. It is not set to be complete until May 2023, nearly five years later than originally planned.

Committee chair Meg Hillier MP said: “The BBC made fundamental mistakes in planning and delivering E20, at significant extra cost to licence fee payers.

“The apparent complacency with which the BBC approached the project is entirely at odds with EastEnders’ strategic importance to the Corporation.

“It was a serious error at the outset not to consider exactly what skills would be needed to see E20 through. The resulting shortfall in key expertise set the tone for much of what followed.

“The revised completion date for E20 is still more than four years away and, as work continues, the BBC must demonstrate it now has a firm grip on the project’s costs and progress.”