Outsourcing firm Serco said it overcame UK and US headwinds to deliver a 12.2% rise in adjusted pre-tax profit, driven by its international portfolio.Adjusted operating profit grew to £133.8m in the six months to end June from £124.4m a year before. Revenue increased 4.9% to £2.24bn. Excluding adverse currency effects revenue rose 5.4%.The group, which runs Dockland Light Railway, said adjusted pre-tax profit rose 12.2% to 123.6m. Earnings per share rose 10.6% to 16.74p.CEO Christopher Hyman said, "Our international portfolio has delivered a good performance in the first half of the year.""Without doubt our markets in the UK and US are facing challenging conditions. However, the breadth of our portfolio, our presence in fast-growing international markets, our significant new BPO capabilities, and the flexibility and innovation of our 100,000 people underpin our strong growth opportunities into the future."At end of June, the order book stood rose to 16.7bn from 16.6bn at 31 December 2010. Serco says it has 98% planned revenue for 2011, 82% for 2012 and 69% for 2013.Serco has declared an interim dividend of 2.5p per share, up 13.6% from 2010.---CJ