A couple found an unexploded Second World War German bomb in their cellar - but waited until the next day to call the police because they did not want to wake the neighbours.

Stephen Sin, from Crystal Palace, London, discovered the explosive while cleaning out his basement on Thursday, in the house he has lived in for 15 years with his wife and children.

The 44-year-old'swife, Janice Hardy, told local paper the Croydon Guardian her husband had not even mentioned the bomb until several hours after it had been found.

“It wasn’t until we were having dinner yesterday and I asked how it went cleaning out the basement and he said ‘Oh, I think I’ve found a bomb’ in a joking way,” she said.

“We decided to do a bit of research, there were markings on the bottom and it said 1936 on the side, we found a picture on the internet that matched it and it tells you it’s a German incendiary bomb.”

Rather than calling the police straight away, the couple and their teenage children moved the bomb into their back garden and decided to wait.

“I had to see some Scouts off to Brussels in the morning,” said Mr Sin, who is a civil servant.

“I thought: ‘It’s been down there for 15 years, another couple of hours isn’t going to matter.”

Germany detonates WWII bombs

Ms Hardy said that she had read an article about somebody who had found a similar bomb, and had heard that it took several hours to diffuse and the road had to be closed.

“So we decided we were just going to sleep on it,” she said.

“To us it didn’t seem like it was going to blow up any moment now, because it hadn’t blown up the whole time we have been here.

“We thought rather than wake up all our neighbours and get them all standing on the street in the dark we decided we would leave it to the morning.”

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During the Second World War, tens of thousands of bombs were dropped on London during the blitz, and though most exploded, some of them did not.

Unexploded bombs, or UXOs (unexploded ordnances) may be duds – they may have been manufactured wrongly and therefore will never explode.

However, some bombs do not detonate due to a fault in the time-delay system, the fuse or other mechanisms. These bombs still pose a serious risk, especially as the mechanisms can disintegrate over time, making the explosive more volatile.

Unexploded bombs tend to be safe if they are left alone, hence their lying dormant for several decades. However, handling a bomb and moving it around can make it more volatile.

As one Army spokesperson put it: “Bombs don’t like to be bashed around.”

The Army advises anyone who finds a bomb to leave it “well alone” and to contact police immediately.

Mr Sin said that, though the situation turned out all right in the end, in hindsight he realised he had been “silly” in his nonchalance about the bomb: