The Ministry of Defence has dumped its target date of 2012 for the first of two giant new aircraft carriers to go into service with the Royal Navy.

It emerged last week that the final decision to go ahead with the project - the so-called main gate stage - may not be reached by the end of this year, as planned.

Defence procurement minister Lord Drayson yesterday told MPs that he had no target date for the main gate to be reached.

He said he was unwilling to commit himself to an inservice date until that stage had been passed and contracts signed with the private companies involved in the deal.

It was confirmed that the minister - the millionaire former boss of vaccine company PowderJect and a major Labour donor - had tried to put off yesterday's hearing until after the contracts were signed.

In a letter to committee chairman James Arbuthnot, he said that the timing of the committee's inquiry into the aircraft carrier procurement was "difficult" as negotiations were at a "critical stage".

If the committee declined to put off its hearing, he warned that the MoD would be "forced to be limited in the information that it will be able to provide".

At an estimated cost of £3.5 billion, the two new carriers are designed to replace HMS Invincible, HMS Illustrious and HMS Ark Royal, which are being withdrawn from service between 2010 and 2013.

The project is expected to create work for up to 15,000 people in the UK and help boost orders for a number of firms, including Derby-based Rolls-Royce.

Invincible has already been mothballed pending its eventual retirement.

The new ships will be the largest in the Navy's history and are expected to be capable of acting as control centres for land forces while moored off unfriendly coasts, giving the armed forces greater flexibility in responding to a range of future threats.

The MoD initially indicated that it hoped to have the first carrier in service by 2012 and the second by 2015.

Lord Drayson, who was appointed a defence minister in May this year, yesterday told the House of Commons Defence Committee: "I have noted the target date which the department has set itself in the past.

"However, given the importance of this project, the inservice date must be set on the basis of the main gate decision. I reserve the right as a minister to set that date on the basis of the main gate decision."

Lord Drayson insisted he intended to proceed to main gate "as soon as possible", but it was not possible to fix a date while complex and sensitive negotiations were under way with the private companies which are joining the MoD in an alliance to build the craft.

It was vital that agreement was reached on how responsibility for the risks, cost and timing of the project would be shared between the Government and its private partners before giving the final stamp of approval.

"I appreciate the concern that failure to pass the main gate would mean this project being delayed. However, this approach, I think, is in the long-term interests of the project and the long-term interests of the Navy," he said.