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* FTSE 100 up 0.5 pct
* FTSE 250 up 0.3 pct
* Oil majors jump on strong crude prices
* Frankie & Benny's owner surges on LFL sales rise
* Weak pound lifts exporter stocks
* Bakkavor slips on Berenberg downgrade
* Interserve climbs ahead of key investor meet
March 15 (Reuters) - Gains by oil majors and optimism that a Brexit delay would help avert a disruptive no-deal departure helped Britain's main stock index rise for a fifth straight day, while Frankie & Benny's owner, Restaurant Group , advanced on strong earnings.
The FTSE 100 .FTSE advanced 0.5 percent and the FTSE 250 .FTMC was 0.3 percent higher by 0826 GMT.
Britain's parliament approved asking the European Union for a short delay if lawmakers can agree on a Brexit deal by March 20, or a longer delay if nothing can be agreed in time. means that for now the prime minister has managed to retain control of the Brexit process and can resurrect her rather battered withdrawal agreement for another vote," said CMC (NS:CMC) Markets analyst Michael Hewson.
Shell RDSa.L and BP BP.L added 1 percent to the main index after U.S. crude prices rose to their highest this year. Production cuts and U.S. sanctions against Venezuela and Iran helped boost prices. weak pound lent support to dollar earners as Prime Minister Theresa May prepared to try again to win approval for her proposed Brexit deal. Diageo DGE.L , the world's largest spirits company, GlaxoSmithKline GSK.L and Unilever ULVR.L all gained.
On the FTSE 250, Restaurant Group RTN.L shares surged 12.2 percent - their biggest rise in two years - after saying like-for-like sales rose 2.8 percent in the 10 weeks to March 10.
Interserve IRV.L shares gained 15.8 percent after slumping as much as 8 percent, before a shareholder meeting on whether to accept a rescue deal or let the troubled outsourcer fall into administration. BAKK.L slipped 6.5 percent as Berenberg cut its rating and said it believes UK food manufacturers are "not as tasty as they look" with shoppers spending more cautiously.