As an insulin-dependent diabetic in the airline industry, I agree with LTNman. My insulin needles are 0.6mm diameter and 6mm long. I have a fountain pen with a fine nib in my kit which would cause more damage. The crew may have over-reacted but equally, may have been bound by their crew operations manual.
Rainboe, you are either mis-informed or being sarcastic.
"...when all around you are having nailclippers and mini-screwdrivers confiscated at security": Are these nailclippers and mini-screwdrivers required to keep you alive?? Blood monitoring and insulin injections are, and, incidentally, would prevent that diabetic passenger from becoming a possible medical emergency during the flight requiring a likely inflight diversion.
"...not exactly onerous.": How would you feel if you had a chronic condition, had to try and get an appointment with your doctor (not exactly an easy task, sometimes), had to get a doctor's letter - not a 'doctor's note' which is required for self-certification and SSP purposes and has nothing to do with this subject - had to pay the (up to) £25.00 that they demand for this "service"/requirement and then have to present it to check-in, security and flight crew whenever asked. Would this not make you feel slightly annoyed. And the galling thing is, when you pass through some airport security stations (LHR T2 and T1 in my recent experience), they do not spot the needles on the scanners and, when you volunteer that your diabetic kit may need checking, they check nothing and point out to you that this is not necessary.
Diabetics are made to feel consistently sub-human by an industry that is increasingly failing it's own low standards of duty of care towards passengers. I would propose to you that this passenger may have had his human rights infringed. I would also ask; was the passenger ever advised by BA that he had to satisfy 2 seperate standards of justification for carrying needles/insulin/blood testing kit? BAA Security (who are contracted by BA for terminal security checks) let him pass unhindered without a doctor's letter. The BA crew demanded that he show them a doctor's letter. A case of double standards, methinks...?