Do bear in mind that St Pancras is a newly renovated station and, as such, fully accessible - and with a lot of facilities, including much better places to wait (possibly with a good meal), whether with coffee in the lobby of the Renaissance hotel, or with a drawn-out meal at the St Pancras Grand (or something a little less substantial at Carluccio's). It's a wonderful building, and one worth taking in (particularly from the upper level).