UPDATE 1-Capita says encouraged by revenue growth

(Adds more detail, comment, background)

LONDON, May 6 (Reuters) - Britain's biggest back-office outsourcing firm Capita Group Plc (CPI.L) said on Tuesday it had performed strongly in the first four months of 2008 and revenue growth across the group was very encouraging.

"Our most active markets remain life and pensions, local government and insurance. We face no material rebids -- greater than 1 percent of the previous year's revenue -- until 2010," Capita said in a statement.

Capita, which runs London's vehicle congestion charge and collects payments from Britain's television licence holders, also said it was "encouraged by the progress of opportunities both in and just outside of the bid pipeline".

The company announces the size of its bid pipeline -- contracts worth at least 10 million pounds ($19.7 million) where it has been shortlisted to the last four or fewer -- twice a year. It stood at 2.5 billion pounds on Feb. 29.

"Our prospects for the current year and thereafter remain strong," the company said.

On Feb. 29, Capita said trading was good amid continuing strong demand for services, as it met forecasts with a 19 percent rise in underlying 2007 profit.

Its shares, which have outperformed other London-listed support services companies .FTASX2790 by 23 percent over the past 12 months, closed at 664 pence on Friday to value the business at 4 billion pounds. London markets were closed on Monday.

Last October, Transport for London said U.S. technology services group IBM (IBM.N) would run London's congestion charge scheme from 2009, after beating two bidders, including Capita. (Reporting by Dan Lalor; Editing by Louise Ireland)