However, during current tightening of security and hand baggage
restrictions, the Department for Transport has advised that you can
only take all essential prescription medicines for the duration of
your flight (up to 100ml of liquid creams or gels, and up to 50g of
powder or tablets).
Essential medicines may be permitted in larger quantities above
this limit, but will be subject to authentication. You must have
obtained the prior agreement of the airline with which you are
travelling and your departure airport. You must also bring
supporting documentation from your doctor or other healthcare
professional.
Most asthma inhalers do not specify how much liquid medicine is
contained within them (they are often measured in puffs or doses),
but as a guide most inhalers contain approximately 10-20ml of
liquid.