The two bombs – one of which was described as “unstable and potentially dangerous” – were cordoned off overnight when they were found by window cleaner Cain Gibson.

But when an Explosive Ordnance Disposal team arrived this morning they had disappeared, fearing a member of the public had taken them away.

Mr Gibson, 23, found the historic shells while out walking his dog by the 16th century Hurst Castle in Milford-on-Sea, Hants, at around 5pm yesterday.

He initially had them in his possession, but then placed them on an old white towel and alerted Hampshire Police who attended the scene.

But overnight they disappeared when they were left unguarded – and today the force was mercilessly mocked on social media for losing them, with people suggesting it was an early April Fools.

Noelle Galfskiy, from Southampton, Hants, said: “Ahhh the good old impenetrable plastic red tape…seems legit. What’s the worst that could happen?

“You couldn’t write this stuff! They must be filming a new Mr Bean movie. Can’t be real.”

Mr Gibson, from Lymington, Hants, recalled: “I was out walking the dog last night over by Hurst Castle at around 4 or 5pm when I found them.

“One was about 12 inches long, the other was about 8 inches, and I had them in my possession for a few hours but then called the police.

“Hampshire Constabulary then came out and took over at about 10.30pm.

“It seems they looked after them for a couple of hours, then went home and the shells were left alone when someone else found them.

“When I left them [the shells], I left them on an old towel.

“The police don’t have a clue where they are. I spoke to the police and they did say it was a bit of a balls up.”

Police are continuing their efforts to locate where the shells have gone over fears they could explode at any time.

But people still saw the lighter side and took the opportunity to mock their efforts in guarding them on the force’s Facebook page.

Ben Holdaway from Romsey, Hants, said: “Let’s just leave these bombs here until the morning……. What could possibly go wrong?”

Paul Mansfield simply wrote: “You left two bombs on the beach unattended? LOL. Idiots.”

And Shirley Youd, from Portsmouth, Hants, said: “But tomorrow is April Fools. Did you get the wrong day?”

A force spokeswoman said: “Two unexploded shells were found at Hurst Spit in Milford-on-Sea by a member of the public last night.

“The shells were cordoned off and plans were made for an Explosive Ordnance Disposal team to attend the site this morning. Unfortunately the shells have disappeared.

“One of the shells has been assessed as unstable and potentially dangerous, so we need to find it as soon as possible.

“Were you walking on the beach early this morning? Did you see the shells or do know where they have gone?”

She added: “If you see the shells you should not go near them. Stand as far away as possible and call us immediately.”

Hurst Castle is an artillery fort established by Henry VIII that later formed part of a network of defences around the Solent during the First and Second World Wars.