This is something that I have always wanted. I do hope that Wargamming puts it in.
One of the things that is actually slightly funny is that thanks to the new HE physics, this tank will be quite the champ at taking artillery rounds, suggesting they hit the roof. This is not by accident, the British designed the top to be artillery bouncy after seeing things like Mark V's being gutted by fire after an artillery strike.
Its gun will really make or break this tank, persoanlly, I'm fine with the weaker 6pdr. Firstly this isn't the 6pdr that you find on the Churchill, sorry. (Though that would be amazing). It's the 6 pounder QF Hotchkiss. A very light naval gun from the late 1880's. Don't let age fool you, shells are still shells. Modified with a longer barrel, this will be enough to deal with Tier IV and lower tanks. At 15 rpm, it wont be the fastest firing gun, however as long as you play smart, should be fine.
Flanking is the obvious way to defeat said flying Elephant as it lacks a turret. Activating it's MG's woulddn't be so effective as they were (probably) Hotchkiss M1909s. That being said, the M1909 is the same gun as the Whippet (Which I personally see as capable of being the British Tier I), so....maybe. Still, they are just Tier 1 machine guns, and would be very low pen/damage. It may provide peace of mind, but tracking with the 6pdr, then just shredding your opponent is the best option.
FE is a slug, so once a tank gets around it, catching up so your main gun and destroy it is just not gonna happen. Again, you will have very heavy armour for your tier, so it may not matter as much. Avoid tank destroyers, Avoid Lee's........tank will do just fine.