Britain's plans to build its biggest-ever warships are being jeopardized by ballooning costs.

The BBC reports it has obtained a memo stating that the costs for constructing two 65,000-ton aircraft carriers have risen by $1.62 billion -- or around 25 percent -- to $8.1 billion since late last year. The memo said the ballooning costs meant a "very real fight for the program's survival."

The aircraft carriers are being built by an alliance including BAE-VT's daughter company BVT, Babcock International, Thales UK and the British Defense Ministry.

The latter is responsible for the majority of the cost increase with its decision to push back the ships' introduction into service by up to two years, the memo obtained by the BBC claims. The Defense Ministry had made the decision to reduce its spending in order to help balance Britain's overall budget -- which faces its biggest hole in decades.

The first of the carriers, which are to hold another British military project, the Joint Strike Fighters, is scheduled to enter service in 2015, with the second one following three years later.

"If you have a longer contract, you pay more," Defense Minister Bill Rammell told BBC Radio. "We don't put forward proposals to invest in equipment unless we think it's necessary."

A Defense Ministry spokeswoman told Defensenews.com that London was "re-costing the program," with formal numbers not to be expected until later this year.

Delaying the two carriers was done to "reprioritize investment to meet current operational priorities and to better align the program with the Joint Strike Fighter aircraft," she said. "We acknowledged at the time that there would be a cost increase as a result."

The carrier program has been questioned many times over the past years, with its critics arguing that Britain does not need the costly warships. The carriers, to be named the Queen Elizabeth and the Prince of Wales, would hold a crew of 1,500, 40 fighter jets and 25 helicopters each.

But senior military officials argue the carriers are needed to keep the British Navy up-to-date, and that's why they lauded the steel-cutting ceremony for the carriers that took place Tuesday at BVT in Govan.

The carriers, together with the Joint Strike Fighter, "represent a step change in Defense's capability, enabling Britain to deliver airpower from the sea wherever and whenever it is required," First Sea Lord Adm. Sir Jonathon Band said in a statement. "This strategic effect, influence and, where necessary, direct action will give us an unprecedented range of options to deal with the challenges of an uncertain world at a time and place of our choosing."

However, the steel-cutting ceremony of course doesn't mean that the program can't be scrapped at a later point in time.