* First-quarter gross premiums written rises 47%, net up 72%
* To return "substantial" portion of earnings to shareholders
* Shares fall as much as 3.6 pct (Adds analyst comments, details, shares)
By Noor Zainab Hussain
May 1Property and casualty insurer Lancashire Holdings Ltd posted a 47 percent rise in first-quarter premiums written, helped by its purchase last year of rival Cathedral Capital Ltd.
Lancashire Chief Executive Alex Maloney, who took the helm last week, said the company was likely to return a substantial portion of earnings to shareholders later in the year.
But shares in Lancashire, which insures oil rigs, ships and aircraft, fell as much as 3.6 percent on Thursday morning amid uncertainty about how much of the company's profits would be returned to shareholders after the purchase of Cathedral.
"... There is a shift in the business model so it makes sense that they may not pay out a 100 percent of earnings, but I still think there are a lot of investors who bought into Lancashire expecting that kind of return," Berenberg analyst Tom Carstairs told Reuters.
A spokesman for Lancashire said the insurer returned about 88.4 percent of earnings to shareholders last year.
Lancashire acquired Cathedral, which insures property, satellites and marine cargo, in August 2013 for 266 million pounds ($449 million), a deal that took it into the Lloyd's of London market.
The British underwriter said gross premiums written rose to $316.7 million in the three months ended March 31 from $214.9 million a year earlier.
Net premiums written rose 72 percent to $204.4 million, while pretax profit fell to $57.4 million.
Lancashire shares fell as low as 675 pence on the London Stock Exchange before recovering a little to 678.5 by 1113 GMT. ($1 = 0.5922 British Pounds) (Reporting by Noor Zainab Hussain in Bangalore; Editing by Robin Paxton)