To take benefit of these prices you will need to prove you are a leisure traveller, en route to the airport, so you will need to give either your flight details or yr holiday booking reference. I don't think you will need to provide this when you arrive at west-hampstead station but you may be asked to provide them on yr journey from west-hampstead station to glasgow-international airport.
Going to glasgow-international airport by train is great, you can take a nap, read a book (even at night), play travel scrabble, or just gaze out of the window... The other restriction to buying these cheap train tickets from west-hampstead station to the airport is that there must be at least two grown ups travelling together. But another great benefit is that children go free. All kids under five go free, and then one child over five but under 16 per adult travelling by train to glasgow-international airport.
make sure you leave enough time to get to glasgow-international airport early enough to eat, shop etc, so check the times of trains from the station before you go. If you end up with time to kill at glasgow-international airport you can always read or play travel scrabble again! As you have bought your ticket in advance, you don't need to worry about the opening times of the station.
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