Once any initial cable stretch has been taken care of, hub gears should seldom need adjustment. However, if you notice any slipping or other odd effects when pedalling, deal with problems as soon as possible to avoid permanent damage. Usually the problem will be caused by poor adjustment, but it could also be caused by a stiff cable run or damage to the indicator chain which goes into the rear axle.

If you cannot resolve the issue quickly, avoid hard pedalling in the gear in question and take your Brompton to your authorised dealer.