"Afraid I won’t be able to contribute anything useful in terms of model experience or tank knowledge." Wanna bet? I have been at these RC tanks for over 20 years, but I still learn from questions people ask, so there is a good chance that a question you ask will teach me something.
OK: what's the difference between a "sea kayak" and one I might (have) used on an inland lake?
Now as to modern British tanks, I suggest not going too cheaply, but not necessarily going to the most expensive. Despite their overall fine quality, Tamiya tanks are not as up-to-date on electronics as some of the ready-made ones. I prefer the Torro tanks (sold also as Taigen here in the US and elsewhere) because of the sound system, as HengLong has only one WWII tank sound. I understand, though, that HengLong can be a bit better for modern sounds, and the steering and low-speed control may be a bit better. (I haven't bought a HengLong for years, but I will soon find out myself.

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Since you are in the UK, your most local seller, Forgebear, is a favorite among RCTW folks. Unfortunately, the Challenger seems to be out of stock now, as you might already know. You might also consider Andrew Haya's Chieftain:
https://www.hayaltd.co.uk/Haya_CHIEFTAI ... 80795.aspx.
I am across the puddle, so for me shipping is always a great factor. I understand that for those in the UK, shipping even from the continent can be expensive, though I don't understand quite why. Here are three sellers whom I have used over the years and found everything AOK, even when the shipping boxes were used by the shippers for football matches.
Licmas, one of my favorites:
https://heng-long-panzer.de/de/RC-Panze ... ition.html
RCTank.de:
https://www.rctank.de/Heng-Long-Challen ... 0S-Platine
Certainly there are more possibilities, and others will likely jump in with advice from closer to home for you.
Join the fun: it's only money.
