Britain must act now over an explosive-laden ‘doomsday wreck’ that threatens to unleash a tsunami in the Thames, experts have warned.

The SS Richard Montgomery sank in the Thames Estuary near Sheerness, Kent, in August 1944, taking some 1,400 tons of WW2 explosives to the bottom.

Her masts still loom above the water line, and plans are in place to remove them, lest they collapse on to the wreck and trigger an explosion – but experts say it’s not enough.

With a new survey revealing the main body of the ship is collapsing, the government has been urged to go further, and remove the bombs themselves before it’s too late.

Professor David Alexander of University College London (UCL) authored a study about the threat of the wreck, and believes removing the masts is insufficient.

He said: ‘I don’t think that’s going to solve the problem.

‘Probably the biggest risk is shipping runs into it.

‘The exclusion zone is 200 metres from a major shipping lane through which large container ships pᴀss and, much more seriously, liquefied natural gas ships.

‘These are five stories high, and contain enormous tanks of liquefied natural gas.’

He cited the example of the Mare Altum, a Danish-flagged chemical tanker that was on a collision course with the wreck when it was diverted with only minutes to spare.

It was one of two near-misses within a single week in May 1980, coming just days after the British-registered MV Fletching came within 15 metres of the wreck.

He also raised concerns about the risk of terrorism and the ongoing decay of the ship.

A 1970 report from the Royal Military College of Science predicted the outcome if the whole explosive cache detonated at once.

It would unleash a column of water and debris 3,000 metres high, and a five-metre tsunami, engulfing nearby Sheerness, the report said.

‘You’ve also got the Isle of Grain,’ said Dr Alexander, Professor of Emergency Planning and Management at UCL.

‘A fifth of the UK’s liquid natural gas comes in through the Isle of Grain.

‘It’s 5.1 km away, and it’s all absolutely ᴅᴇᴀᴅ flat. It doesn’t have any particular coastal defenses either.’

The ‘whole forward section of the wreck’, which lies in two halves on the bottom, ‘appears to have an increase in lean’ of 10 to 15cm

In a statement, the Department for Transport said its priority was to ‘ensure the safety of the public and reduce any risk posed by the SS Richard Montgomery’

Dr Alexander called on the government to clear the ship of explosives.

He said: ‘I think it is worth doing because I’m not convinced that it is becoming safer, and I’m not convinced that it is safe now.’

It’s a view shared by David Welch, formerly of the Royal Navy, now a senior explosives officer at bomb disposal company, Ramora.

Though he believes it’s ‘nigh on impossible’ for the whole cargo to detonate at once, he warned that the explosives won’t be contained for much longer.

He said: ‘I do think that someone’s going to have to do something soon, in the next decade, or we’re going to miss the boat.’

He added: ‘The wreck is falling apart, as all wrecks do, and munitions are falling out of it.

‘Over time, that’s only going to get worse and then you’ll end up with an uncontained area of munitions.

‘There’s small fishing vessels in the area, there’s all sorts of other activities, and you don’t want these items to become lost.’

He continued: ‘If you fast forward 100 years, the likelihood is the wreck won’t be there, but the pile of munitions will.

‘At the moment, you’ve got everything stacked relatively neatly in a structure that still has some integrity and therefore you could stage a clearance operation.

‘As soon as the wreck falls apart and all those munitions spread out on the seabed, it’s much more challenging.’

Dr Alexander called on the government to clear the ship of explosives. He said: ‘I think it is worth doing because I’m not convinced that it is becoming safer, and I’m not convinced that it is safe now’

He argued that the cost of leaving it could be a growing exclusion zone in the Thames Estuary.

He said: ‘I don’t think there’s an argument, certainly not in that part of the world, to say let’s give up four or five acres or hectares of seabed, or whatever the area might be.’

He added: ‘You can leave it forever if you want, but future generations are going to have to deal with it.’

It comes after a recent survey found further signs of collapse in the ship, all observed in the previous year.

These included the ‘whole forward section of the wreck’, which lies in two halves on the bottom, leaning 10 to 15 cm further eastward as ‘supporting sediment is eroded away’

A spokesperson for the Department for Transport, the responsible ministry, said the wreck was under constant monitoring

 It’s feared the wreck still holds enough explosive power to unleash a tidal wave in the Thames, earning her the nickname ‘Doomsday wreck’

A crack along the second cargo hold had also grown 5cm wider and 37cm longer since the previous survey, and was ‘significantly buckled’ further down.

The back half of the ship, meanwhile, was ‘potentially breaking in two about halfway along its length’, with a stretch of deck six metres long collapsing over half a metre in one year.

A spokesperson for the Department for Transport, the responsible ministry, said the wreck was under constant monitoring.

They said: ‘Our priority will always be to ensure the safety of the public and reduce any risk posed by the SS Richard Montgomery.

‘We commissioned experts to carry out vital surveying work and we continue to monitor the site 24 hours a day, and undertake detailed surveys to ᴀssess the wreck’s condition.’

In its statement, the department added that there was ‘no indication’ that the further degradation of the ship ‘has increased the risk’ ᴀssociated with it.

They also highlighted the much-delayed plan to remove the masts, saying they would work with a contractor to create a revised plan, anticipated ‘within the next year’.