To take advantage of these 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 your flight numbers or your 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 yr journey from the station to the airport.
Going to heathrow 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 inexpensive train tickets from the 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 five go free, and then one kidover 5 but under sixteen per grown up travelling on the train to heathrow airport.
be sure to leave enough time to get to heathrow airport early enough to eat, shop and so on, so check the times of trains from milton-keynes-central station before you go. If you end up with spare time at the airport you can always read a book or play a game again! As you have bought yr train ticket in advance, you don't need to worry about the opening hours of the station.
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