It is currently not possible to make a seat reservations outside of Britain but mainline National Rail stations will be happy to make reservations for you when you arrive Britain.
Caledonian Night Sleeper reservations can be made in advance through their call centre +44 141 555 0888. Please note Caledonian Sleeper reservations can only be made if you hold the full BritRail Pass and no other pass in the BritRail range. (When you have purchased your BritRail Pass and want to make the reservation, ensure you advise the call centre staff you hold a BritRail Pass.)
Night Riviera Sleeper reservations need to be purchased at the station.
When making an advanced reservation at the station before your travel date, you will need to present your BritRail Pass as proof you hold a valid ticket but will not need to validate it, unless you are travelling that day or it has started already.
For more information contact our BritRail specialist agents.