Apologies, Bit of a short one today, as I'm off on Honeymoon, and don't have much time.

Earlier in the year I was combing the Archives and tucked away in the back of a document about the FV201 series, unseen for a number of years due to miss-filing, I found a few pages talking about a tank I'd never heard of. Having a lot to do that day I quickly took some photo's and got on with it.
Under later review I realised I'd found documents talking about a brand new infantry tank, a replacement for the Churchill. Which would make this mystery vehicle the Infantry Tank MKV, if it made it off the drawing board. In the documents it was only known by the initials "WB1".
(When discussing this find with a few others I jokingly claimed the right of naming my discovery, and named it after my fiancée. It fits British tank naming conventions, her name is Claire)

Myself and Vollketten from the US server have been plugging away at this problem since then and we have a few more sources to check, but we've generally drawn a blank. No one, and I mean no one has heard of it. Even the librarians at Bovington haven't heard of it.
Googles contribution to searching for WB1 Tank, and that's a propaganda poster with a Churchill MKII
So here's what we know at the moment.

On 14th of May 1948 the General Staff issued a specification for a new 70 ton tank. The date is interesting when you consider that the Black Prince had already been halted, and had previously carried a 17 pounder gun. The specification called for a tank with a speed of 20 mph and an engine giving a power to weight ratio of 0.75 BHP per ton! It was required to have a 100 mile operational range.

A43 Black Prince
The performance was largely decided by its armour. The specification called for 400mm basis through the frontal 60 degree arc. The specification talks a lot about sloping, so its safe to assume that the tank would be well angled. Roof armour was to be immune to guns up to about 5.5" calibre if the shell was to detonate within two feet of the roof, and the belly was to be resistant to 25 pound mines.

Armament was to be a gun of at least three inches and capable of penetrating 125mm of armour at 30 degree's of slope at the range of 2000 yards. You'll remember in my earlier article about the Conqueror that the British were having trouble rationalizing what to do about guns on tanks, although the choice of a three inch weapon was made at the start of this period of indecision.
The HE and smoke capabilities were to be at best the same level as the current 77mm gun. 80 rounds of ammunition was to be carried along with a single co-axial machine gun.

Another oddity was the requirement to have full climate control and protection against chemical and biological weapons, along with infra red equipment for night time driving.

On the 22 of June 1948, A.E. Masters, the Chief Engineer at the FVDE replied having reviewed the specifications. His first conclusion was that the armour requirement of 400mm was impossible, and the best that could be obtained was only 350mm basis. Side armour was to be about 100mm.

On the gun front he states that he used the current 77mm gun in his review, and checking other sources you can see that APDS from a 77mm has the required performance against armour.
The reply from Mr Masters highlights something interesting. He was having trouble fitting all the components into the tank. First off the biggest engine they could get in due to the weight requirement was something about the size of the Centurions engine, and so the top speed would be limited to about 17 mph. Equally the good cross country performance ate into the size of the crew compartment, which meant they were looking at a rather cramped interior.

After that, there's not a lot else on the subject. We're still looking though!