If you are planning a trip to London and haven't yet bought travel insurance, it's likely too late to get coverage. Most policies exclude destinations (often countries, not just cities) where a terrorist incident has occurred within the past three to six months.

If you are planning on traveling to London within the next month and already have a travel-insurance policy, you're covered for canceling under standard trip-cancellation and trip-interruption clauses in policies issued by companies such Access America and CSA, two of the nation's top three insurers.

Each policy varies, but the standard wording on terrorist attacks abroad (most policies also cover domestic terrorism) is that the attack must take place in a foreign city in which you are scheduled to arrive within 30 days — unless you're on a tour or cruise and the operator offers a substitute itinerary.

In Washington State, TravelGuard's "ProtectAssist" plan covers only areas where the U.S. State Department has issued a warning. Travel Guard is the nation's largest travel insurer.

"The biggest concern is if you get a policy that covers you only if the State Department issues a travel warning," said Jim Grace, CEO of InsureMyTrip.com, a Rhode Island-based online seller of travel insurance policies. "The problem is that there is none right now (for the United Kingdom) and probably won't be."

The U.S. government (see www.travel.state.gov for information) now has 29 countries on its warning list. Most are Third World countries or in the Middle East.

The U.S. Embassy in London yesterday advised Americans to defer all non-essential travel to London until further notice, but as of last night, the State Department's Web site contained no updated warnings or advisories.