I know the MPAA or whoever aint gonna come knockin at your door for backing your HDD up to gmail, but gmail may terminate your account if you fill their mailbox up quickly
As for TV programmes... BBC wont be hosting the programmes, its usually hosted by individuals on websites etc, so BBC wont have to pay for bandwidth, therefore could let it go that people are downloading their programmes instead of watching it on TV when it was originally on.
As for programmes like Friends and ER which are re-transmitted on Channel 4 - they may not be legal to download... Friends in particular as it is available on DVD. ER isnt owned by Ch4, so like I mentioned Neighbours earlier... same could apply.