im not exactly sure where cherry jam is But if your looking for a bed
go to picadilly backpackers its at picadilly circus, sherwood St. Its £11 for a bed for a night, its clean.. got showers... clean... trendy I always stay there when im in london... its central and has 24 hour reception
you may have to just check there website for what they say about people under 18.
If your after a hotel... There is the National (I think) at russel Square. Its £40 for a twin bedded room im pretty sure