The rules are clearly stated:

Question
Do passengers with diabetes need to make any special arrangements to travel on BA flights ?

Answer There is no reason why someone with insulin dependent diabetes cannot fly as a passenger. For longhaul flying (particularly if crossing time zones) it may be sensible to discuss how you manage your insulin regime with your healthcare professional.

Diabetic passengers do not require advance medical clearance to travel on British Airways flights provided their condition is stable and they can take care of their own medication requirements. If you are unable to administer your own medication and are travelling alone then you will need to fly with an escort who is willing and able to assist you.

British Airways are unable to store insulin in aircraft fridges for various reasons. Diabetes UK (formally known as the British Diabetic Association) advise that insulin, in general, can be kept at room temperature (below 25 degrees C) for up to a month without losing its effectiveness. Further information is available from Diabetes UK at www.diabetes.org.uk.

Passengers should carry a letter from their doctor confirming the need to carry syringes, needles and medication in the aircraft cabin. As security screening at airports is outside the control of British Airways, you should discuss a contingency plan with your Doctor to enable you to travel safely in the unlikely event that the authorities do not allow your equipment to be carried in cabin baggage.

Please note: The above information applies to passengers who need to carry syringes, needles, epipens and medication, in their hand luggage, for any medical reason.

Battery operated glucose monitors may be carried in hand luggage. If you are carrying these monitors you must obtain a Doctor's letter confirming your need to carry 'sharps' on board an aircraft.

If this chap travels as often as he claims to do then he ought to be aware of the rules...which begs the question...how effective is the security screening if this has not been picked up before?