Gerald Seymour: A Line In The Sand, A [2000] paperback

In a village on the Suffolk coast Frank Perry waits for his past to arrive. A decade before, he spied for the government on the Iranian chemical and biological weapons installations. The information he provided damaged the Iranians' killing capacity for years. Now Iran will have its revenge, and has despatched its most lethal assassin to fulfil the task. Code-named the Anvil, he will move with stealth and deadly commitment towards his chosen objective, unless Perry's protectors can reach him and stop him first. As he draws near, the ring of steel protecting Perry grows tighter. But against a faceless adversary, and with the job fatally compromised by the stifling bureaucracy surrounding it, there seems little chance that the past will not have its day once more...