Irish Republican Army attacks are making insurers leery of covering London office buildings. The Association of British Insurers is urging its members to drop all but modest terrorist coverage as of Jan. 1. Insurers were alarmed by the discovery of a huge bomb in the heart of the Canary Wharf complex on Nov. 15. Disarmed by police, the device could have wreaked enormous damage on the office buildings. Insurers say they face a payout as high as $1.4 billion from an IRA bombing in the City of London last April. Scores of anxious companies, from Imperial Chemical Industries PLC to Guinness PLC, now plan to lobby the government for a state-run insurance plan similar to one that is provided for those doing business in Northern Ireland.