Two and six speed Brompton bikes use a proprietary Brompton derailleur system. Here you can find all the controls, for example shifters / triggers, gear cables, derailleur mechanism for your bike.
Replacement chain tensioner assembly for Brompton bicycles with a derailleur (2 speed or 6 speed) This can be identified by the fact it has 2 identical looking black jockey wheels where the chain sits in a groove in the jockey wheel.
Brompton derailleur chain tensioner idler (jockey wheel) bearings / fixings set - pair - QCTIDLDRSET
Replacement Brompton derailleur chain pusher dog leg assembly (QCHPULEGA)
Replacement Brompton derailleur spring assembly set - pre-2017
Brompton 2017 derailleur gear shifter with integrated brake lever - Black Colour: Black
Replacement Brompton derailleur chain pusher assembly
Replacement Brompton derailleur cable anchorage and spring set - complete - for integrated gear shifter Note: for 2017 model Bromptons onwards (introduced late 2016)
Brompton derailleur gear trigger / bell assembly complete - pre-2017 version
Brompton 2017 derailleur gear shifter with integrated brake lever
Brompton derailleur gear cable only, M Type, excluding dog leg section For pre-2017 model Bromptons
Brompton derailleur gear cable only, S Type, excluding dog leg section For pre-2017 Brompton derailleur system
Brompton derailleur gear cable only - excluding dog leg section - pre 2017 model For H type Brompton with long wheel base.