Hi and Happy New Year all.
I just returned from Mexico. Had a wonderful time. Great country, great food and amazing, welcoming people.
I know this thread is old but just thought I would update to say the landing card is as basic as it's ever been and does not ask about convictions. The "check" with the border agent is non-existent, they just robotically stamp your landing card and passport without even a glance, and without asking any questions. Maybe it helped that we landed very late at night and they seemed half asleep.
Obviously I did not go through the US. Sorry to hear about the difficulties some have experienced, seemingly thanks to the US. Annoying that you would have permission from the UK authorities to go to Mexico but then the US decide that you should not go to Mexico and dob you in to them despite it having nothing to do with the US. Luckily there are plenty of direct flights from Gatwick/Heathrow or alternatively stopovers via other European airports like Paris and Madrid.
My conviction is not drug-related.