Copepod is right, according to this BBC article
http://news.bbc.co.uk/1/hi/health/7637374.stm:
"Some people with diabetes and high blood pressure are to be allowed to donate blood for the first time.
A committee of experts has ruled it is safe for these groups to give blood, even if they are taking medication to control their condition.
However, donors must have no complications or underlying medical conditions - and people taking insulin for diabetes remain barred.
There were concerns that donating blood might compromise diabetes medication.
In the UK almost one in 20 people has diabetes, and increasing numbers are being diagnosed with the type 2 form of the condition, which mainly affects adults.
However, the majority manage their condition by taking tablets and most are fit and healthy.
However, to ensure that it is safe to give blood donors have to fill in a health check questionnaire and talk to a trained member of staff before pressing ahead.
Dr Lorna Williamson, medical director of NHS Blood and Transplant, said: "Type 2 diabetes and high blood pressure are diagnosed in increasing numbers of people.
"Many were regular blood donors who were saddened when they had to stop donating.
"Guidelines are in place to ensure safety of both donors and patients.
"The committee regularly reviews new evidence and that has shown that it is safe for them to donate so this restriction has been lifted."
Libby Dowling, of the charity Diabetes UK, said: "We welcome these new guidelines and are pleased that some people with diabetes are now eligible to donate blood if they wish to.
"There are 2.3 million people with diabetes in the UK and these new regulations mean that a significant proportion of people with the condition can now help save lives by donating blood." "
I have written to the National Blood Service and when they reply I will let you know.