LONDON (Reuters) - Britain has cut rental fees by up to 90 percent in its latest tender for oil and gas licenses in the North Sea launched on Wednesday in a bid to attract companies to find new fields in the mature basin.

Companies will now be able to apply for cheaper and more flexible licenses to gain access to 1,261 blocks by Oct. 26, followed by license awards to be issued by the Oil and Gas Authority (OGA) at a later date.

The hunt for new oil and gas fields in the British part of the North Sea is expected to fall to the lowest in 45 years this year as energy companies have scaled back exploration budgets due to weak oil prices.

Despite being an old basin, Britain's North Sea is estimated to have billions of barrels left for extraction, worth around 200 billion pounds ($262.56 billion) to British government coffers.

The latest licensing round, the 29th, offers access to new areas in the Rockall Trough, the mid-North Sea High and East Shetland, which were subject to a government-funded seismic testing campaign earlier this year.

"We recognise that market conditions are currently very difficult but nevertheless we have a shared goal of making the basin as attractive as possible for exploration," Andy Samuel, chief executive of the OGA, said.

The Oil and Gas Authority's contract changes will reduce license rental fees in some cases by up to 90 percent per square kilometer and allow explorers more flexibility in terms of when they can carry out certain work programs.

Companies which obtained licenses in last year's bumper 28th licensing round, Britain's biggest ever, included Shell <RDSa.L> and Eni <ENI.MI>.

(Reporting by Karolin Schaps. Editing by Jane Merriman)