The Royal Navy's £6 billion fleet of Type 45 destroyers is spending more time berthed in UK military ports than on active duty defending the nation, official figures have revealed.

The six vessels notched up a staggering 1,515 days in our harbours in the year between April 2015 and 2016 - and four of the state-of-the-art ships were stationary for more than 300 days each.

The figures, obtained through a Freedom of Information request, have angered a former head of the Royal Navy, who has called for urgent action by Theresa May to resolve the problem.

Harbour: Type 45 destroyers HMS Dragon, left, and HMS Diamond which can been seen docked up in Portsmouth earlier this year

The Ministry of Defence has insisted the fleet was not 'sitting idle' and was meeting 'operational tasks'.

The MoD also dismissed accusations the ships were at port to save money.

However Admiral Lord Alan West, the former First Sea Lord, was not convinced and said more needed to be done to improve the situation.

He said: 'We desperately need to get the destroyers out and doing their job.

'We are using Royal Fleet Auxiliary and offshore protection vessels to do jobs that historically would have been done with frigates or destroyers.'

Many of the vessels have faced significant periods of maintenance and refit, with one - HMS Dauntless - now being relegated to a £1bn 'training ship'.

The fleet were also encountering engine problems in the Gulf, and improvements are being made.

Lord West added: 'It seems to me that because we have so few ships that the "get-well package" for the destroyers needs to be implemented with absolute full speed to get them fully available for operations.'

Prize ship: The Royal Navy's £6 billion fleet of Type 45 destroyers is spending more time berthed in UK military ports than on active duty

The ship which has spent the longest time in a UK port between April 2015 and 2016 is HMS Dragon, which was based at Portsmouth Naval Base for a total of 330 days - but this came after a nine-month deployment.

HMS Daring - which sailed from Portsmouth on a nine-month mission this month which will see her joining the fight against ISIS - spent 319 days in the UK.

And after completing a five-month tour in May of last year, HMS Dauntless spent seven months in refit and has not left Britain since, now operating as an engineering training vessel.

HMS Diamond, which deployed to the Mediterranean this month, also spent more than 300 days in the UK.

It was in maintenance and refit before spending two months from May to July this year on operational sea training and further maintenance.

HMS Duncan and Defender spent the least amount of time in the UK, with 125 days and 132 respectively, after having both recently returned from nine-month missions.

The revelations come as the navy faces an engineer recruitment crisis, delays in the replacement programme for the aging Type 23 frigate fleet and issues with the Type 45s' unreliable engine system.

Lord West denied claims the heavily-armed air defence fleet was 'stagnating' in UK ports, but said the Navy was faced with a critical shortage of manpower and cash that urgently needed to be addressed.

He said: 'There is clearly a real problem over money in the Navy - there's not enough of it.

Port: Type 45 destroyer HMS Diamond docked up in Portsmouth earlier this year

'There is a shortage of money and the government has got to come clean about it.

'We need to get cracking and do the repair work that is needed.'

Maritime expert Lieutenant Commander Mike Critchley, now retired, said the figures show the situation with the destroyer fleet had worsened, adding the 'desperate shortage' of engineers was compounding the issue.

Lt Cmdr Critchley, of Gosport, said: 'This has been going on forever.. .it's just getting worse as the days tick by.

'If we had more engineers in the Navy we could have these ships out at sea.

'But you can't just click your fingers. This is a long-term issue that needs a lot of planning.'

A MoD spokeswoman said: 'We are meeting all of our operational tasks and our destroyers are not sitting idle.

'Ships operate out of ports while they go through high-intensity preparations for operations and while they conduct crucial defence engagement.'

We desperately need to get the destroyers out and doing their job Admiral Lord Alan West

The MoD said its target of having 60 per cent of the destroyer fleet at sea would be met with the latest round of missions.

A five-year overview of the destroyers' capacity to be at sea would be a fairer assessment, the MoD added.

Penny Mordaunt, Portsmouth North MP and former armed forces minister, said she expected to see the destroyers out at sea more in the coming years.

'The situation has improved considerably over the last year, latterly with only one ship in at a time for maintenance,' she said.

'Some ships in harbour have been doing training alongside, and we want to see as many out on ops as possible.

'The improvements have come with better management of spare parts and an improving manning situation.

'Resolving the problems of the Type 45 engine and propulsion systems has also assisted greatly.'

The Navy's Type 45s, also known as the D or Daring class, are an advanced class of six guided missile destroyers built - at a cost of around £1bn each.

The class is primarily designed for anti-aircraft and anti-missile warfare, and the first to be built - HMS Daring - was commissioned in 2009.

They replaced the Type 42 destroyers that had served during the Falklands War, with the last of their class being decommissioned in 2013.

During an attack a single Type 45 could simultaneously track, engage and destroy more targets than five Type 42 destroyers operating together.

On the launch of HMS Daring, the Royal Navy proclaimed it was the world's best air-defence ship.