Well I phoned a local store (the place I ordered the drill from is closed) and asked them to check and of course the chuck should fit a 13mm bit.
Not hugely impressed that I spent £450 on a drill and can't use a 13mm drill bit!
I know I can return but too much hassle. May and try and get them or Festool to send a new chuck on its own.
I buy Festool so don't have to have these hassles - poor quality control.