To take advantage of the best prices you will need to prove you are a leisure traveller, en route to stansted airport, so you will need to give either your flight numbers or yr holiday booking reference. I don't think you will need to provide this when you arrive at the station but you may be asked to provide them on your travels from the station to the airport.
Going to stansted airport on the train is great, you can take a nap, 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 brent-cross station to the airport is that there must be at least two grown ups travelling together. But another great benefit is that children go free. All children under five go free, and then one child over 5 but under 16 per grown up travelling by train to the airport.
make sure you leave plenty of 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 yr ticket in advance, you don't need to fret about the opening hours of brent-cross station.
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