The blast sent shards of metal flying more than 50 feet.

Detectives said that if anyone had been driving past at the time, they could have been killed.

Bomb disposal experts are investigating how the sturdy 10-foot-tall piece of equipment on the A605 at Thrapston, Northamptonshire, was wrecked.

Had someone been driving past at this time, the occupants would have been seriously injured or killed and we could have been looking at a murder inquiry Det Con Alison Farr

The incident is the latest in a series of deliberate attacks on speed cameras across the country, which has been blamed on frustrated motorists.

Dozens of cameras have been burned, toppled and driven into, but the A605 camera was believed to be the first that had been bombed.

Detective Constable Alison Farr, of Kettering CID, said on Tuesday night: "We are treating this crime extremely seriously, it was an unbelievably irresponsible act.

"The force of the explosion forced metal right across the road and had someone been driving past at this time, the occupants would have been seriously injured or killed and we could have been looking at a murder inquiry."

Police appeal

A team from the Explosive Ordnance disposal unit has examined the site and forensic experts have also studied the debris.

A spokeswoman for Northamptonshire Police said the incident happened between 0001 GMT and 2225 GMT on Saturday.

She appealed for anyone who saw the explosion or anyone acting suspiciously in the area to contact the police.