A family found an unexploded German bomb in the basement of their home – then waited overnight before calling the police because they did not want “wake up all the neighbours”.

Stephen Sin, 44, and wife Janice Hardy, 52, uncovered the 1930s incendiary device as they cleared out the cellar of their Crystal Palace house yesterday.

The couple, who have lived in their Patterson Road house for 15 years, reported the bomb to the police this morning – but only after running errands and doing some work.

Mr Sin, who is self-employed, said: “We knew that this was going to happen, where literally everything stands still, so because I had to see some Scouts off to Brussels this morning I thought: ‘It’s been down there for 15 years, another couple of hours isn’t going to matter’.”

A police expert later established the bomb – thought to have originally been made in 1936 for use in the Spanish civil war before being dropped on London during the Blitz – was not live.

The couple, who have two teenage children, moved the device into their back garden and researched it online after making the discovery – which Ms Hardy only found out about herself after several hours when he husband causally mentioned it over dinner.

The civil servant said: “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 found a bomb,’ in a joking way.

“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.

“They designed them for the Spanish Civil War and I can only assume that they had some many left over that come the Blitz they decided to just chuck them all over the UK.”

The couple initially feared the device might force the police to put their road on lockdown.

Ms Hardy said: “I saw this piece from the Mail Online about someone finding a bomb that looked just like that bomb.

“It said it took several hours to blow it up, they had to put a 200 metre cordon around the house, close the road so we decided we were just going to sleep on it.

“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 and work out who to ring and what we are going to do.

“But it turned out all alright in the end.”

Mr Sin described the discovery of the bomb as “not your typical day” but said he had been “quite calm” about finding an explosive device in his basement.

He added: “I was just putting all the metal stuff together, there was pipe work, odds and sods like boiler stuff and then there was this bit that hand a kind of fin and I thought, ‘That doesn’t look like something you would get from a house.’ “So I just put that to one side, as you would. It’s not your typical day.

“Because we have lived here for 15 years we just thought ‘nah, this is silliness’.

“I was quite calm because it looked so old, which is silly of me looking back at it.

“You can’t actually fathom it until after, then you think: ‘What if it had exploded?’ “People would probably think ‘he was a decent bloke, but what a prat’.”

The Metropolitan Police said officers were called to Patterson Road at 1.20pm today "to reports of World War Two incendiary device around 40cm long".

A spokeswoman said the device, which officers took two hours to remove from the garden, was not thought to have posed a threat.