The RN drugs policy is pretty rigid with regard the individual's attitude to drugs & is entirely inflexible if there are criminal convictions related to Class A drugs prior to joining.
That said, it's accepted that the majority of individuals experiment with drugs in some sort of way shape or form prior to joining & it would negate about 50% of viable applicants if we ruled them out entirely - the issue is habitual or excessive drug use prior to joining.
Those that need to see their GP or visit A&E regarding recreational drugs use & have it recorded on their medical records would quite possibly bear further investigation prior to being passed fit for entry.
Sadly convictions for the trafficking or supply of drugs are a permanent bar to entry in the Armed Forces, but not necessarily the House of Commons.
It is an accepted fact that graduates are proportionately more likely to have habitually used drugs, whether that's why we let them run the country & indeed the Armed Forces is open to conjecture :wink:
The issue is the inviduals attitude to recreational drugs, not whether they have taken them previously. If you still think it's fine to take banned substances then you're in for a surprise if you wish to serve in the Armed Forces.