Later this year i have a trip to England and I am looking for advice around getting through British customs without an issue.  While I don't expect problems it makes sense to ask for advice in case anybody has been through it.
The options I see are:  
I could dress as a guy but, well, that's increasingly hard to pull off and if they scan or pat down then that goes out the window.
Alternatively I could travel like a proper young lady but, my papers still have the dreaded M on them.  I would hope this would not be an issue but I could see where a security focused country like England might have a problem with not matching my passport. 
The last item and my current "safe" plan is to dress male so I match paper description and bring a letter from my therapist that says I am trans.  
thanks in advance.