http://www.heathrowairport.com/heathrow-airport-guide/heathrow-security/faqs#carriageofmedicines
Medicines
Can I take medicines in my hand baggage?
You can take enough essential liquid, aerosol or gel medicines in your hand baggage to cover your journey plus a reasonable amount to cover any delays. Any liquid, aerosol or gel medication not needed on the flight, together with any spares must be packed in your hold baggage.
There are no security restrictions on the carriage of powder or solid based medicines.
Liquid, aerosol or gel medicines in containers of 100ml or less should be either:
- Placed inside your single transparent, resealable plastic bag no larger than 20cm x 20cm, along with any other liquid items; or
- Carried separately together with supporting documentary proof of authenticity such as a prescription or letter from your doctor.
Liquid, aerosol or gel medicines in containers over 100ml must be carried separately, together with supporting documentary proof of authenticity, such as a prescription or letter from your doctor.
At security, you must present all liquid, aerosol and gel medication for inspection. Following x-ray screening, security officers may also need to carry out additional checks on these items.
The rules above apply equally to homeopathic and children’s medicines.
There is no requirement to contact the airport in advance of your travels.
http://www.gatwickairport.com/at-the-airport/flying-out/security/faqs/
I need to travel with medicines and medical equipment – are the rules the same for me?
Passengers are allowed to take essential medicines sufficient for their trip. Amounts under 100ml should be placed in a transparent, resealable plastic bag, with any other liquids. If the container is larger than 100ml it should be presented at security for x-ray inspection. There is no limit on the amount but all medicines will be subject to additional security screening and you will be asked to provide proof such as a doctor's letter.
Passengers may carry non-prescription tablets (e.g. paracetamol), but as with all other medicines they should be properly marked with a professionally printed label identifying the medication and manufacturer's name or pharmaceutical label.
Any other medical item that you may need during your flight – including insulin and needles, asthma inhalers, Epi Pen, angina sprays etc. – can be carried, but only the amount necessary for your trip. The rest should be put in your hold baggage.
If you are concerned about the effect of the temperature in the aircraft hold on your medicine, you should speak to your airline directly.