Mystery as Royal Navy's £3.1bn aircraft carrier HMS Queen Elizabeth set to slink back to Portsmouth at 4am

HMS Queen Elizabeth is due to sail back into Portsmouth exactly three weeks after she left to tackle her latest set of trials with the F-35 stealth jet in the North Sea.

It is the shortest time the 65,000-tonne behemoth has spent at sea with the F35s, with previous tests with the state-of-the-art jet in America having lasted five weeks.

The Royal Navy has insisted the movement had always been ‘planned’ and declined to comment on whether the surprise return was due to an unexpected fault on the ship.

A spokesman said: ‘HMS Queen Elizabeth is making her planned return to HM Naval Base Portsmouth in the early hours of Friday morning.’

While the ship’s official Twitter account released a message to its 80,000 followers – hours after The News contacted the navy – saying: ‘After a successful period at sea we will challenge ourselves further as we attempt to make the first night entry into #Portsmouth.’

However, one senior naval source said the move to bring in the ship was bizarre and claimed it could indicate a fault had been identified that was too difficult to fix at sea.

‘The fact that she is sailing in either means there’s a defect on the ship that precludes her doing flight trials and or there’s something wrong with key safety systems on the ship,’ the retired senior officer told The News.

As previously reported, Queen Elizabeth’s departure last month had been delayed by several days following a reported issue with the ship’s generator.

Last year, the ship suffered a major flood and lost propulsion off the coast of Devon, which prompted an unexpected return to Portsmouth for repairs.

The News understands dockyard workers were today scrambled, with many due to be called back to the base just after midnight to prepare for Queen Elizabeth’s early-morning arrival.

Queen Elizabeth was spotted yesterday off the coast of Lowestoft, East Anglia, some 200 miles away.

To make the trip back to Portsmouth, the ship is expected to be travelling ‘at speed’, the source said.

‘They’re keen to get her back in if they’re coming back in at night in what will be reasonably strong winds,’ the officer added.

The news comes as Britain braces itself to be battered by winds of up to 70mph and heavy rain over the weekend.

Amber weather warnings have already been issued by the Met Office as Storm Dennis trundles towards the UK.

Winds are expected to reach almost 60mph in Portsmouth, which would make it challenging for Queen Elizabeth to safely navigate through the city’s narrow harbour entrance if she were to return any later than tomorrow.

Meanwhile, there has been no word on when Queen Elizabeth’s sister ship, HMS Prince of Wales will head to sea.

The navy had announced on Tuesday afternoon the vessel would set sail on Wednesday but promptly cancelled the move a few hours later with no explanation.

It’s understood Prince of Wales is still scheduled to visit Liverpool on February 28, where she will stage a weekend open event, giving the public the first chance to step on board a Queen Elizabeth-class carrier.

Speaking about Queen Elizabeth’s return home tomorrow, a spokesman for the Royal Navy said: ‘HMS Queen Elizabeth is making her planned return to HM Naval Base Portsmouth in the early hours of Friday morning.’