I have a staff travel pass for GWR, and I'm looking to travel to London on the sleeper at some point in the summer. I'd be travelling with someone who does not have a PRIV, so would have to pay full price standard fare. I was wondering if it would be possible for us to both pay a £35 supplement for a 2 bed berth, as it would work out cheaper to do it that way. I can't work out whether I'd be able to pay just the £35 for a supplement using my pass in lieu of a ticket, or if I'd have to buy a normal priv rate ticket, then pay the supplement. If anyone knows some info would be much appreciated.