Finding living accommodation in London.

Two of my graduate grandchildren have new jobs starting very soon in London. Being on entry level salaries they are both searching for reasonable accommodation, either together or apart. This is proving to be very difficult. Any place coming up on line is either already taken or a viewing time is arranged at which 100 or more people turn up! Many hours a day are spent searching the internet or travelling to these viewings, as they currently live in Oxfordshire. Commuting will be their only option if they find nothing, but this would have to be temporary.
Has anybody any hints or leads which would help them please?
GNHQ has given me permission to post this.