Marex used to be Refco Trading Services, they are one of the better prop firms in London and they do have a good number of backed traders, you'd just need to be very good with a proven record for them to be interested.
Are you backed somewhere at the moment? Who have you spoken to already?
You could look at Schneider, Kyte, Elite Derivatives, or one of the many lists of London prop firms as they are almost exclusively futures, unlike US props.