Broadgate is one of the few, if not the only, outdoor ice skating rinks in London (and it's tiny). The venue's season starts in early November and typically ends in the beginning of April. Admission costs 6BPs for adults and 4BPs for children. Skate rentals are 2BPs and 1BP, respectively. No lockers are available to rent, so you'll have to keep an eye on your things. It's very near the Liverpool Tube station within the Broadgate Mall. See their website for more details.