Bear in mind that HR departments generally have no record of what they did yesterday, let alone what they did with a graduate offer from last year. There are no bridges to be burned, as they’ll completely forget who he was this time next week.
I applied for a graduate job with Airbus. When through a rather arduous two day selection process, but got rejected. Two months later they call me for an interview, seemingly having forgotten about the two day selection process I failed. Got offered the job (which I declined for other reasons).
Two options have merit. Take the £5k and start the hunt again (inc. applying for the same job in 2025). Keep the offer and carry on looking for a job at the “big 3” or elsewhere. £5k isn’t a lot of money, so I would go with the latter option.