I can't recall what the contract says but the comapany seems to have a fairly relaxed attitude to standbys. Due to the nature of our work we are rarely called out at the last minute. You are normally informed a few days in advance that you will be working on a standby.
a lot of BMed crews (both flight deck and cabin) live some distance away (Bristol, west country - even some in spain and Holland. The company does not seem to get too troubled by this.