THE North-East's biggest ever terrorist attack could have been averted, but for blunders by the intelligence services, according to ex-spy David Shayler.

The allegations are contained in a book by the former MI5 agent, who was jailed in 2002 for revealing intelligence service information to a newspaper.

Mr Shayler, from Redcar, east Cleveland, claims MI5 had a film of terrorist Sean McNulty at an IRA safe house, in 1993, 11 days before he used Semtex to blow-up a gas-holder, in Gateshead, and the Esso Oil Terminal, at North Shields.

However, in the book - which he co-wrote with his partner Annie Machon - he claims the pictures were not acted on until it was too late.

Appearing on Saturday at a book signing in Guisborough, east Cleveland, Mr Shayler, 39, said: "It has been incredibly hard to get this book published. There is still a huge amount of opposition to us getting this information out there. In the end, it took 15 months to get it cleared."

Mr Shayler observed McNulty's movements for 18 months leading up to the attack, at first believing he was a low-level IRA operative.

No one was hurt in either of the incidents and McNulty was jailed in 1994 for 25 years for causing explosions aimed at killing and bringing terror. He was released in 2000 as part of the Good Friday Agreement.

Mr Shayler and Ms Machon worked together for MI5's political and counter-terrorism departments in the 1990s.

Since they left the intelligence services, both have become keen activists and anti-war campaigners.

The book entitled Spies, Lies and Whistleblowers: MI5, MI6 and the Shayler Affair is out on May 10.