Each Brompton leaves the factory with a unique identifying serial number.
For pre-2013 bikes, the serial number can be found on the back of the seat tube below the seat clamp.The serial number consists of a silver sticker with ten digits and a barcode.
The first four digits of the serial number correspond to the year and month in which your bike was built; the first two refer to the year and the second two refer to the month.
The frame number can be found stamped onto the frame as shown below:
For 2013 bikes and newer, the serial number sticker has moved lower down the seat tube. The frame number remains in the same place.