Catlin made a net operating loss of $220m in the first half of 2011, down almost 500% on the $57m profit it posted during the same period last year.

The Bermuda-based insurer blamed the loss on $534m in catastrophe losses sustained in the first half.

Catastrophe losses also caused Catlin’s combined operating ratio to jump 19 percentage points to a loss-making 116.5%, from a profitable 97.5% at 30 June 2010.

Gross premiums written for the six months ended 30 June 2011 increased by 9% to $2.7bn, up from $2.5bn at 30 June 2010.

Gross premiums written by the Bermuda, US and international underwriting hubs increased, whilst the insurer continued its objective to reduce gross premium volume in the competitive UK marketplace.

Catlin chief executive Stephen Catlin said described the group’s performance during the period as “strong” despite the significant losses.

Catlin also announced the impending retirement of chairman Graham Hearne at the annual general meeting in May 2012. Hearne will be replaced by John Barton.