Both the CAA and BA have looked at this quandry. The reality is that pilots as a group are far more healthy than the general population and the risk of incapacitation is very very low. Most people are not inherently dishonest and the UK has a general practitioner service where all an individual's notes are coordinated. In fairness Germany is an outlier in putting laws in the way of doctors communicating with each other.
Mental health may be different but there is scant evidence of this and it is difficult to have any mental health assessment or treatment without your GP knowing. The CAA then carefully makes it difficult for a pilot not to disclose.....Personally I think we are about right: we seem to be avoiding mental health issues putting flights at risk and any further restriction would therefore have little benefit but would inconvenience pilots.