The listing at 310 pence per share values the company at about 581 million pounds ($965 million), making it the largest biotech IPO since at least 1995, according to life science publication EP Vantage.

The next largest IPO in the sector was Ark Therapeutics which raised 55 million pounds ($91.3 million) in London in 2004.

Circassia is raising 200 million pounds ($332 million) before costs in its share sale to help bring to market a vaccine for cat allergies. In addition existing shareholders are selling shares worth 9 million pounds, the company said.

The price range for the offer had been set at 250 pence to 310 pence. Conditional trading will start at 0800 GMT on Thursday.

JP Morgan Cazenove and Peel Hunt were joint book runners on the offer.

Biotech saw a renaissance in the United States last year with dozens of listings, but it remains to be seen whether the trend can be replicated in Europe.

Many firms opt for the tech-focused Nasdaq exchange rather than a European listing, in order to access capital from investors experienced in the biotech industry. Britain's Lombard Medical this week decided to delist from London and switch to Nasdaq with an $80 million IPO there.

The sector has proven to be highly volatile in the past, as seen with the sudden rise and fall of experimental cancer drug firm British Biotech in the 1990s, while Ark Therapeutics has lost 99.6 percent of its share value since its debut.

($1=0.6022 pounds)

(Reporting By Freya Berry; Editing by Greg Mahlich)

By Freya Berry