Us insurer Quincy Mutual (Quincy) has received a Financial Services Authority licence to write all categories of general reinsurance.
The move will enable Quincy to operate throughout Europe. Initially, the company will focus on a short-tail, non-marine account.
General manager and senior underwriter John Warwick said: "We have been low-key in setting up. Too many people have been shouting about what they can do in this market."
Quincy received its licence on November 24 last year, but did not announce the fact.
Warwick said: "We can do a decent job for the small to medium-sized companies. We haven't got £100 million capacity but we have got a really good, solid client base."
Warwick said that Quincy has been operating as a UK contact office for its US parent since November 1998. This, he said, has allowed the reinsurer to build up its client list.
But Quincy's entry into the market has surprised some industry experts. Analyst Eamon Flanagan of Charterhouse said existing poor market conditions could hamper Quincy's progress.
He said: "It is a brave move because the market is quite fluid at the moment."