To take advantage of these prices you will need to prove you are not a business traveller, en route to stansted airport, so you will need to provide either yr flight numbers or yr holiday booking reference. I don't think you will need to give this when you arrive at forest-hill station but you may be asked to give them on your journey from the station to the airport.
Going to the 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 caveat to buying these inexpensive train tickets from forest-hill 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 five but under sixteen per grown up travelling on the train to stansted airport.
be sure to leave enough time to get to the airport early enough to eat, shop and so on, so check the times of trains from the station before you go. If you end up with spare time at stansted 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 worry about the opening hours of the station.
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