Amateur explorers have put their lives on the line, crawling into wartime tunnels in danger of collapsing.

Hair-raising video shows two in an area with decaying beams groaning under piles of rocks high up in a cliff.

They even clamber down the near-sheer drop of a cliff to reach the entrance.

Horrified coastguards, who were shown the film, say the young men were lucky to get out unscathed.

And event the two seasoned adventurers involved have admitted that this experience was so frightening and dangerous they will never go to that spot again.

One, David Cripps, who described the place as "Hell's mouth" told Kent Online: "It was seriously dangerous. We would not recommend anyone going there and we are not going there again."

David Cripps and Mark Hallett were filmed going into the tunnels in a video released by the Abandoned World Explorer UK YouTube Channel.

They explored tunnels cut high into Dover's western cliffs above the Samphire Hoe nature reserve, used by soldiers during the Second World War.

Mr Crips said: "We enjoy exploring. We are 100% adventurous. We started this five to six months ago and we get a lot of followers on YouTube.

"But in this case the entrance to those tunnels should have been closed off. There was also a footpath on that cliff, which I think was too steep."

Mr Cripps, 36, of Rochester, is a teacher on a year out and Mr Hallett, 36, from Strood, works for a betting shop.

Other places they have explored include flooded 1860s fortifications at Shorne, Gravesham. But the structure the were inside was solid and the floodwater shallow.

The 23-minute film at Dover, called Welcome to the Death Hole... shows them in an area called Lydden Spout between Abbott's Cliff and Samphire Hoe.

Mr Cripps and Mr Hallett start at the top of the cliff and the gradient is so sharp they have to climb down on their backside.

The entrance, to a military deep shelter used in the Second World War, is high up on the cliffs and is so narrow they have to crawl in.

At the entrance rotting wooden beams hold up piles of chalk rocks further in rotted door frames do the same.

The film shows some areas of chalk ceiling already collapsed.

Deeper in, the ceilings are high enough to stand and walk in and there are tunnels lined with corrugated iron, some leading to living quarters.

The tunnels deeper in appear more solid. But steep steps, which eventually lead back to the top of the cliff, are slippery through being soaking wet with damp and moisture.

A large ventilation pipe, originally attached to the ceiling, is collapsed and lying on the floor and handrails have rotted away.

Without their torches the place is pitch black.

But the two men, taking turns to film each other, also find wartime graffiti, with the names of soldiers carved in and the year of their presence, for example 1941.

The men show their trepidation regularly through their dangerous adventure and finally emerge unharmed.

Mr Cripps then remarks on the film: "We're out of Hell's mouth."

The men had a third person waiting outside the tunnels in case of emergency.

Graham Easton, senior coastal operations officer for HM Coastguard, said: ‘The footage of these young men climbing precariously down the cliff to access these unstable tunnels is alarming - they’re incredibly lucky that they didn’t fall down the cliff and that the tunnels didn’t collapse whilst they were inside.

"Had this happened inside the tunnels they may not even have had a mobile signal available to alert us. It’s no doubt they’ve had a lucky escape on this day."

"We want people to enjoy themselves on the coast by making sure their visit is one to remember and not one they’d rather forget."

The Maritime and Coastguard Agency stresses that cliffs all along the UK coastline are continually eroding and pieces that fall from them can by anything from smalls rocks to those as large as a car.

It stresses that there have been a number of cliff collapses around the UK coastline in recent months and visitors should stay far from the edge.

Some cracks can be several feet away.

Mr Easton added: "Don’t be tempted to go and investigate and don’t risk going to the edge to get a dramatic picture.

"One of our biggest problems is tackling the selfie culture where people take risks to get a dramatic photograph of themselves on a dangerous cliff edge.

"No selfie or photograph is worth risking your life for."

Those in trouble at cliffs or seeing someone else in difficulty should instantly call the Coastguard on 999.

The Maritime and Coastguard Agency offers the following general safety advice for the coast:

Be properly equipped on coastal paths. Wear sturdy shoes or boots and check the weather forecast and tidal times before setting out.

Carry a fully charged mobile phone and tell someone where you are going and what time you will be home.

Only use the designated paths, take notice of warning signs and fences and don’t take unnecessary risks.

Do not try to climb up or down cliffs unless you are properly equipped and trained.

Do not attempt to climb cliffs as a short cut back to the top.

When standing at the bottom of a cliff it is best to stand less than the height of the cliff away.

That means that if the cliff is 25 metres high, don’t go closer than 25 metres towards it.

Try and keep your dog on a lead near cliffs.

They could wander towards danger if they pick up the scent of an animal or hear something on the coast below .

Above all, if your dog does fall down a cliff or starts getting swept out to sea, do not try to rescue it yourself.

Nine times out of 10 dogs save themselves and return to shore alive.

Coastguards are trained in dog and all other types of rescue.