Authorities believe the brazen slaying of a Canadian biker, who was shot dead on a busy English highway as he left a motorcycle festival, was a "pre-planned" attack.

Gerald Michael Tobin, 35, of south London was riding the M40 through the central England county of Warwickshire when he was killed in broad daylight on Sunday afternoon, British police said in a statement.

Earlier that day, Tobin had been at the Bulldog Bash motorcycle festival at Long Marston airfield.

Warwickshire Police Det. Supt. Ken Lawrence said that a green Rover 600 series car, with two or three people inside, started following Tobin and two other motorcyclists as they returned from the festival.

Several kilometres later, the green car overtook two of the three motorcycles and came close to Tobin.

The car was travelling at more than 112 kilometres an hour when shots from within the vehicle were fired at Tobin.

Two shots are believed to have been fired, and one of those struck Tobin on his head just below his helmet. Tobin fell off his motorcycle, which continued to career another 200 yards down the road. The green Rover kept driving.

Autopsy results show Tobin died of a single gunshot wound to the head.

Tobin, who had lived in the U.K. for 10 years, worked at a Harley Davidson dealership in south London as a mechanic.

Lawrence described Tobin, who was in a stable relationship, as a "hard-working" man who was of "good character."

Tobin is believed to have been a member of the Hell's Angels motorcycle gang.

Police said there was nothing in Tobin's past to indicate why he had been targeted but that it seems clear the shooting was planned rather than a random attack.

"It seems likely that this was a pre-planned event and this was not a random attack on Gerard," Lawrence said.

"It certainly appears to have been reasonably well-planned in that if that car in the lay-by was in fact there waiting for him to pass... if that was waiting for him, expecting him to take that route, then of course, that does indicate some prior knowledge."

However, Lawrence suggested there may have been "an element of chance" involved as he found it "difficult to believe that someone was that good a shot".

Warwickshire Police said they had already received more than 200 calls from the public with information about the shooting.

However, they urged any more witnesses to come forward who saw the green car or Tobin's black Harley Davidson FXSTB motorcycle.

Warwickshire police are also reexamining a similar six-year-old case.

It was on the same stretch of road in 2001 that a Canadian was shot as he rode home from the Bulldog Bash. He was wounded in the leg but recovered. The gunman was never found.

Every summer, the Hells Angels stage the popular Bulldog Bash, which attracts approximately 40,000 motorcyclists from around the world for a four-day party at the Long Marston Airfield, near Stratford-upon-Avon.