Please note that I have just extracted the following from the Heathrow Airport Security guidelines for passengers:
"Passengers are allowed to take essential medicines sufficient for the trip. I am concerned about the temperature of my medicine in the hold. Yes, you may carry esssential medicines for the trip. However, you may be asked to taste any liquid medicines, or to provide evidence (such as a doctor's letter) that you need them for your journey."
I don't want to undermine what the what some of the well intentioned posters have written, but if you ignore what the airport's own website advises, then you do so at your own risk.