The mortar bomb Ian Platt pulled from the canal (Photo: Yorkshire Magneteers)

Ian Platt was pursuing his hobby with the Yorkshire Magneteers on the Calder & Hebble Navigation in Dewsbury when he made the extraordinary find.

Mr Platt and his team sealed off the area before West Yorkshire Police made an official cordon while they waited for the arrival of ordnance disposal experts.

Magnet fishing is the act of searching in outdoor waters for magnetic objects which are available to pull with a strong magnet.

Sign up to our daily newsletter The i newsletter cut through the noise Sign up Thanks for signing up! Sorry, there seem to be some issues. Please try again later. Submitting...

This hobby, which is a combination of environmentalism and treasure hunting, has grown rapidly in both the UK in recent years.

It's not the first time Mr Platt, who lives in south Leeds and works as a barman in the city centre, has pulled out potentially deadly material from the waters.

Last year, he and friend Dave Pearce, from Roundhay, pulled out a mammoth 18lb mortar from the Boer War from under Crown Point Bridge.

Having learnt from past experience, Mr Platt knew what to do this time.

Mr Platt just before he pulled the bomb from the water (Photo: Yorkshire Magneteers).

"I knew what it was straight away," he said. "I shouted 'mortar bomb' and everybody ran.

"We went about 50 yards in each direction and cordoned the area off.

"The police took a picture and sent it to the Royal Logistics Corp and they said it's definitely a World War Two device.

"They turned up and said it was definitely live. It was only 2lb but it had the potential to cause a bit of damage so they put it in a special container and drove it away.

Dave Pearce and Ian Platt when they pulled out a bomb from the River Aire in Leeds.

"The thing is, kids going fishing around there. If a kid had pulled it up, they wouldn't have known. Anything could have happened."

The area was cordoned off for around three hours on Sunday afternoon.

Since being set up by Mr Pearce around a year ago, the Yorkshire Magneteers membership has rocketed to around 800.

The hobbyists are trying to make their operation as professional as possible given their huge growth.

In Yorkshire, they have been given permission from the Canal & River Trust (CRT) to carry out their hobby without any need for a licence, as they are effectively helping clear the canals for free. Earlier this month, they pulled 1.3 tonnes of scrap from a waterway in Knottingley.

Several World War One machine guns were found in Rotherham last year.

If the trial is successful, the CRT is considering rolling it out across the country, Mr Platt said.

The magneteers are sent high-power magnets from sponsors in China, who are eager for their products to be featured in their video footage.

"It's gone huge," Mr Platt said. "It's grown into a real community."