Finance bosses have warned that the British capital risks losing its appeal for stock market listings, after Softbank-owned chip designer Arm said a U.S. IPO was its best option and materials giant CRH decided to move its primary market listing across the Atlantic.

"What we're really keen to do is to create the right environment so companies like Aviva can survive and grow," Aviva CEO Amanda Blanc told reporters after reporting results.

Blanc said planned reforms to capital rules for insurers - known as Solvency II - were an important step and would unlock 25 billion pounds ($30 billion) of extra capital the group could invest in infrastructure over the next decade.

The decision by Arm to only list in New York showed a "holistic effort" was needed to reverse the decline in Britain's share of global company stock market listings, the chair of regulator the Financial Conduct Authority said on Wednesday.

Andrea Rossi, chief executive of asset manager and insurer M&G, said Britain needed to better support new companies to attract them to London's stock market.

"What's important is to be able to have growth equity to support these early stage businesses throughout their journey to a potential IPO - that is not something only linked to the UK, but it's overall in Europe," Rossi told Reuters.

"Generally, it's American players - clearly, they are the ones that provide growth equity [and] they will probably bring afterwards these firms into the U.S," Rossi said after the firm's earnings.

Rossi said while he was "bullish" on Britain's prospects, the country needed regulatory and political stability after a turbulent end to 2022.

Britain's finance ministry said on Wednesday it will launch a review into how investor research on companies could be improved to attract more listings.

($1 = 0.8408 pounds)

(Reporting by Iain Withers in London and Sinchita Mitra in Bengaluru, Editing by Alexander Smith)

By Iain Withers and Sinchita Mitra