Find a small - but perferably busy - airfield which has volunteers on the radio.
This might be a good idea for someone who is just generally inexperienced or nervous about RT, but the poster is comfortable with RT in the US, just not in the UK. Visiting one small airfield won't get you used to zone transits, MATZ penetration, flying at a controlled airfield etc, so is of very limited use in this case.
How many units was this tested with? Was it tested outside the UK? For starters, Timothy would have had a Mode C transponder. Did he tell them it was an Aztec or did he pretend to be a Warrior?
The idea was to try the different combinations, with the junior pilot in both a rented PA28 and Timbothy's Aztec, then Timothy in both planes too. They were going to try Thames and Luton and a couple of others. However, the junior guy in the PA28 got let through everywhere so they never did the rest of the flights. It was published in Flyer, though I expect the big man himself could furnish you with the details.
Not that my own experience proves anything but I've never heard someone with poor RT being denied a transit and within a short amount of time someone with good RT being granted one.