Martin Clough, 32, escaped on Monday afternoon while on a trip to Leeds from Wealstun Prison, near Wetherby.

A spokeswoman for West Yorkshire Police said: "He is not dangerous but we would like to trace him as soon as possible."

Clough was given a discretionary life sentence in 1986 for aggravated arson.

He was told by the Parole Board last July that he could apply for release in nine months time.

But in August, Home Secretary David Blunkett extended that time to 15 months.

Clough recently challenged that decision in the High Court but the judge has yet to deliver his ruling.