To take advantage of the best prices you will need to prove you are not a business traveller, on the way to the airport, so you will need to provide either yr flight numbers or your holiday booking reference. I don't think you will need to give this when you arrive at norwich station but you may be asked to provide them on your journey from norwich station to the airport.
Going to luton airport by train is great, you can sleep, 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 norwich station to the 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 5 but under sixteen per adult travelling on the train to luton airport.
make sure you leave enough time to get to luton airport early enough to eat, shop etc, so check the times of trains from the station before you go. If you end up with spare time at luton airport you can always read a book or play travel scrabble again! As you have bought yr ticket in advance, you don't need to worry about the opening times of the station.
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