Do you need a letter to get through airport security

I went to Australia last month and was advised to get a letter from my doctor stating my condition and that I needed my blood glucose monitor and lancets. Cost me £10 for the letter but glad I did cos I was stopped at customs after they put my hand luggage through and they wanted proof that I needed the lancets. Not sure what they thought I was going to do with a needle that short!
Anyway, worth getting the letter cos you never know how anal they are going to be about it!!
Nicki