To take advantage 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 yr flight details 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 provide them on your journey from the station to heathrow airport.
Going to the airport by train is great, you can take a nap, read a book (even at night), play travel scrabble, or just stare out of the window... The other caveat to buying these cheap 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 child over five but under sixteen per grown up travelling by train to the airport.
be sure to leave plenty of time to get to heathrow airport early enough to eat, shop and so on, so check the times of trains from crewe station before you go. If you end up with time to kill at heathrow airport you can always read or play travel scrabble again! As you have bought your train ticket in advance, you don't need to worry about the opening hours of crewe station.
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