Dublin, which is seeking to become a major EU financial centre, has already attracted several insurers planning EU subsidiaries in the event that British financial firms can no longer sell their services across the bloc.

"Since the referendum announcement we have been clear that our top priority is to provide certainty and consistency of service to our clients and brokers. Moving XL Insurance Company SE to Ireland means we deliver on that commitment," XL Chief Executive Officer Mike McGavick said in a statement on Tuesday.

The firm operates under the "Societas Europaea" structure, which means it is registered in accordance with EU corporate law, making it relatively easy to move its European base.

XL Group has had insurance operations in Dublin since 1990, and also set up an Irish domiciled reinsurer in 2006, it said.

XL Group would keep its Catlin Insurance Company and its Lloyd's of London [SOLYD.UL] operations in Britain, it added.

XL would increase staffing in Dublin to "70 or more" by the end of 2018 from about 45 now, a spokeswoman said in an emailed statement. "We are not planning for relocations - a few people will initially commute regularly," she added.

Insurers surveyed by Reuters this week said they would move or create around 100 jobs in the EU as a result of Brexit, but some declined to comment on staffing numbers.

Trade body Insurance Ireland and development agency IDA Ireland welcomed the decision by Bermuda-registered XL Group.

(Editing by Edmund Blair)

By Noor Zainab Hussain and Carolyn Cohn