Would your carry-on have any liquids or gels or creams of any kind?

Travelling ex-UK, all of the above are not allowed through security. So if you have those in your carry-on, they will be chucked away !

Security is extra stringent and loooong especially at LHR these days especially for connecting passengers.

75 minutes is cutting it - especially if your flight from MUC has a long taxi to the gate. Most flights from Germany to UK are rarely on time. If you miss your flight, then UA would have to accomodate you accordingly. Don't know what they'll do though.