In my past life I was Head of Aviation Security at London Luton Airport and sat on the Joint Airports Security Committee.
I have to agree that different Airports adopt differing rules and these vary between individuals who carry out the screening. Many Airports now use different Contractors rather than employ their own in-house staff.
However, all standards should in theory be the same, as all airports are required to adopt the CAA rules and all screeners should be trained to the same standard. However that is not the case in practise.
My advice is always to advise the airline and airport in advance of your needs and to carry a Doctors letter and Prescription list. If needed, this can be produced at the screening point if necessary. You can always request a hand search of any equipment and if a body search is required, you can request that this is carried out in private away from others.
Without saying too much. The Catch 22 problem for the screener is that those who seek to hurt us can be very devious and can use items of equipment to conceal dangerous things. This is why certain items of equipment have to either be x-rayed or if not they would need to be taken apart to see what may have been secreted inside. Hence the Doctors letter helps.
Unfortunately screening is an absolute neccesity in the current climate and ultimately the security search team can refuse you to travel. For this reason, It is best not to get angry with them at the time. It may be worth asking to speak with the Duty Security Manager who will be well versed in the procedures for diabetics.
If your experience dosn't go well, it is always worth bringing to the attention of the Civil Aviation Authority (CAA) via their Website as they are responsible for setting the standards in the UK and feedback is essential.
With regards to The Landyard Scheme - This is operated at some Airports including Heathrow, Gatwick and Bristol by OCS. It is designed to help people with disabilities get through the airport more easily and with less worry. OCS staff can recognise the Landyard and offer assistance with help on Checking In or Preparing your bag prior to Security Screening. It will not negate any of the requirements of the Security Screen or Check In Procedures or get you through any faster. It is basically a helping pair of hands.
Hope that helps a bit.