Eye of the Storm — Jack Higgins

Former allies in the IRA, Sean Dillon and Martin Brosnan have chosen different paths. Now Dillon is a terrorists for hire, a master of disguise employed by Saddam Hussein. Brosnan is the one man who knows Dillion's strengths and weaknesses...and brilliant mastery of espionage.
Once friends, now enemies, they are playing the deadliest game of their careers. A game that culminates in a frightening - and true - event: Iraq's attempted mortar attack on the British war cabinet at 10 Downing Street in February 1991...