Sean Creighton, 44, of Coventry, had previously denied killing the 35-year-old mechanic from, Mottingham, London, but changed his plea.

Creighton also admitted firearms offences.

He will be remanded in custody and will be sentenced at the end of the trial of six other men accused of the murder, which is expected to last between six and eight weeks.

Karl Garside, 45, pleaded not guilty to killing Mr Tobin and to firearms offences at a hearing in February while Simon Turner, 41, Dane Garside, 42, Malcolm Bull, 53, Dean Taylor, 47, and Ian Cameron, 46, entered their not guilty pleas for the same offences in December.

The full addresses of the defendants, who are from Coventry, Nuneaton and Milton Kenyes cannot be reported for legal reasons.

Mr Tobin was riding his Harley Davidson motorcycle along the M40 near Leamington on August 12 2007 when he was killed by a single gunshot wound to the back of the head.

He had attended the Bull Dog Bash biker festival at Long Marston Airfield and was travelling home.