To take advantage of the best prices you will need to prove you are not a business traveller, en route to glasgow-international airport, so you will need to provide either your flight numbers or yr holiday booking reference. I don't think you will need to give this when you arrive at the station but you may be asked to give them on your journey from the station to the airport.
Going to glasgow-international airport by train is great, you can sleep, read (even at night), play a game, or just gaze out of the window... The other restriction to buying these inexpensive tickets from the station to glasgow-international airport is that there must be at least two adults travelling together. But another great advantage is that children go free. All children under 5 go free, and then one child over five but under sixteen per adult travelling by train to the airport.
be sure to leave plenty of time to get to glasgow-international airport early enough to eat, shop and so on, so check the times of trains from the station before you go. If you have time to kill at the airport you can always read a book or play travel scrabble again! As you have bought your train ticket in advance, you don't need to fret about the opening times of the station.
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