Oasis' Liam Gallagher has apologised to fans for this week's (June 4) show at Manchester's Heaton Park, which saw the band leave the stage twice due to technical difficulties.The rockers were offstage for a total of around 40 minutes following a stuttering start to the 70,000-capacity gig due to a generator failure.They offered refunds to fans after returning to complete a full 23-song set. Pic: Danny North