Dmytro Firtash, the Ukrainian trader who has emerged as a key player in the European natural gas market, was unfamiliar to most western business people until this week. But a small group of British businessmen have known him well for years.

When he appeared last year at a Mansion House dinner at which the Queen presented an award to Ukrainian President Viktor Yushchenko, the 40-year-old Mr Firtash sat at a table hosted not by Ukrainians, but by JKX Oil and Gas, a British AIM-quoted company with interests in Ukraine.