Around 358,000 Britons carry adrenaline auto-injectors (AAIs) to deliver a shot of adrenaline should they suffer a potentially life-threatening allergic reaction to food - commonly milk and peanuts, medicines- such as antibiotics and chemotherapy drugs, or insect stings.

AAIs with brand names EpiPen, Jext and Emerade, are prescribed for people who have either experienced an anaphylactic reaction or who are susceptible to high-risk allergic triggers such as peanuts. 

In some cases, one shot of adrenaline is required, but if the allergic reaction is severe, two may be necessary. According to the charity Anaphylaxis Campaign, despite the recommendation of the Medicines and Healthcare products Regulatory Agency to carry two AAIs at all times, around 10% of people may only be carrying one. 

Concerns are also being raised by doctors and campaigners about where to administer the injections. Previous advice was to make the injection into the muscle on the outside of the thigh but the question being raised is whether the second dose - administered five minutes after the first if needed - should be in the same or different leg.

Adrenaline works by narrowing the blood vessels and, in the case of anaphylaxis, helps to restore heart function and blood pressure which can drop dangerously low. The concern is that if adrenaline is injected into the same leg twice, the second dose will have little effect as the blood vessels there will already have narrowed.

This issue was raised at the inquest of the London teenager Natasha Ednan-Laperouse, who died after eating a Pret a Manger baguette containing sesame to which she was highly allergic. When Natasha had the anaphylactic reaction her father administered two doses of adrenaline into her right outer thigh , but the drug didn't work. At her inquest, consultant allergist Dr Alex Croom said this could have been because both shots were given in the same leg.

GP And TV presenter Dr Mark Porter said on social media: 'The second dose should not be given in the same spot, as adrenaline causes vasoconstriction (reduced blood flow), which could impair absorption of the second dose. So always use a different site. Using the opposite thigh is a simple way to ensure this.'