Eye of the storm by Jack Higgins

The source provides excerpts from a novel detailing an elaborate assassination plot, primarily centered on the elusive professional mercenary, Sean Dillon. Dillon is contracted by Michael Aroun, who is working with disgruntled KGB Colonel Josef Makeev on behalf of Saddam Hussein, to assassinate the British Prime Minister, Mrs. Thatcher, after a failed attempt at a French airfield. The story also tracks British intelligence operative Brigadier Charles Ferguson and his American confidant, former IRA member Martin Brosnan, as they attempt to track Dillon, utilizing Brosnan's past connections with the mercenary. A subplot involves a Soviet mole, Tania Novikova, who is feeding Dillon's handler, Makeev, classified British security information. Dillon eventually carries out the attack using a makeshift mortar devised by an old accomplice, Danny Fahy, before fleeing to a French airstrip owned by Aroun, where he anticipates his payment but is instead betrayed.