Lots of crew live in the Oxford area, it is an easy drive down the M40. It is well within the 2 hours to the carpark for a Home Standby - only SH do airport standby. There are no standbys for LGW as such unless you are SH, the 777 does fly from LGW but all pilots for the 777 are LHR based and special rules apply to LGW reports, so if called from sby for LGW they can still only expect you to be at 2 hours to the LHR carpark - they may ask you to try to be at LGW asap but it is not a requirement.