Go to expireddomains.net, go to "pending delete" and filter on .co.uk domains. There you see that you can backorder through 123-reg.co.uk and catchtiger.com. I don't know if there are more companies. Search on namepros or google for more topics around this.
A backordered domain does not keep his age. The domain has expired and will be registered as soon as it is expired by a dropcatcher. Therefore, it counts as a newly regged domain.