Media playback is unsupported on your device Media caption The Type 45 destroyer is one of the most advanced anti-aircraft warships of its kind

The Royal Navy's most modern warships are to be fitted with new engines because they keep breaking down.

In an email seen by the BBC, a serving Royal Navy officer wrote that "total electric failures are common" on its fleet of six £1bn Type 45 destroyers.

The Ministry of Defence said there were reliability issues with the propulsion system and work to fix it would be done to ensure "ships remain available".

One Royal Navy officer said the cost could reach tens of millions of pounds.

In a statement, the MoD told the BBC that to "address some reliability issues" it was considering options to "upgrade the ships' diesel generators to add greater resilience to the power and the propulsion system".

That will involve significant work, though the Royal Navy insists that the six destroyers will still be deployed all over the world.

'Major weak link'

But from 2019 each will begin to undergo a major refit that will probably involve cutting a large hole to insert at least one new generator into the ship.

The work will be staggered to ensure the Navy still has ships to send on operations.

The MoD would not give any details on cost.

Admiral Lord West, a former First Sea Lord, said the development was "very worrying" and the MoD must have known "three or four years ago" that the destroyers had problems.

The ex-Labour security minister said any delay in rectifying the problem would leave the Navy's surface fleet badly stretched, as the Navy can already "only just do some of the tasks we should be doing around the world".

"What I would hope is there is already in place a 'get well' programme and we must move very quickly to rectify these problems," he said.

A former naval officer, Rear Admiral Chris Parry, said the problems could not continue: "It's rather like buying a high-priced television to watch your favourite football team but because you don't have secure power supplies, the power goes off about every 10 minutes.

"You can't have that in combat, you can't even have that in normal operations - it is not safe."

'The lights went out'

Image copyright PA

I experienced one of the many power outages on board HMS Dauntless, off the coast of Senegal, in 2012.

Suddenly all the lights on the ship went out. It was quickly fixed but it appears to be a problem that has plagued the entire fleet.

In 2014 Dauntless had to abandon a training exercise and, in 2009, HMS Daring lost power in the Atlantic on her first voyage to the US. She suffered more propulsion problems off Kuwait in 2012.

Initially the MoD dismissed these electrical failures as "teething problems".

But it has now admitted that there is a bigger problem - one that could be disastrous for a ship and her crew in combat.

Nick Childs, of the International Institute for Strategic Studies, said: "It's an unfortunate extra cost the Royal Navy will have to swallow to sort out an unreliable propulsion system - the major weak link in an otherwise world-beating system.

"They're essentially going to have to squeeze in an extra generator to improve reliability."

The warning signs were there in 2009 when the Commons Defence Committee published its report on the Type 45.

MPs noted "persistent over-optimism and underestimation of the technical challenges, combined with inappropriate commercial arrangements" leading to rising costs.

Each destroyer ended up costing about £1bn. The Royal Navy wanted 12 ships but ended up with half that number.

The Type 45 has an integrated electric propulsion system that powers everything on board.

'World's most capable'

The problem won't be solved quickly and it is likely to put a strain on the Royal Navy, which has already shrunk considerably in size.

It is now down to a surface fleet of 19 frigates and destroyers.

A spokesman for Rolls-Royce, which makes the WR-21 marine gas turbine used on the warships, said the company continued to work with the MoD on upgrading the performance of the propulsion system.

BAE Systems, the company which builds the warships, said in a statement that the destroyers were "among the world's most capable air defence destroyer".

It said it was working with the MoD "to deliver improvements to the power generation capability of the Type 45 destroyers".