LONDON (Bloomberg) — Businesses in New York, London and Brussels are struggling to buy insurance against terrorist attacks at affordable prices as demand for the policies rises world-wide, according to insurance brokerage company Aon Corp.Businesses in Manhattan in New York and Canary Wharf in London are among “terrorism capacity hotspots” where it’s “difficult to obtain cover at acceptable prices for new risks,” the Chicago-based broker, the world’s second biggest, said in a report on its web-site yesterday. Companies that are trying to buy so-called stand-alone terrorism-insurance policies in the cities are the ones that are struggling for cover, the report said.

Insurers are less reliant on US-based customers to buy policies amid “huge growth” in demand from the rest of the world for the products, it added.

At the same time, as prices in the cities are stretching affordability, insurance premiums globally have fallen because underwriting capacity has climbed by about 20 percent since January 2006 to $1.5 billion, as investors are lured by the industry’s premium-to-claims ratio, the report said.

Underwriting capacity is the amount of money that insurers are prepared to place at risk. The more it increases, the more money there is competing for premiums, forcing prices down.

The world’s biggest insurance broker is New York-based Marsh & McLennan Companies Inc.