The 55 divisions is OTL, but the UK was only to supply 36 of them - the other 19 would be from the Dominions & India. OTL, the UK reached its 36-division target in 1941-2, but was unable to maintain it when heavy fighting resumed in 1943-44, finishing the war with only about 24-25 divisions, some of them severely under strength. (In 1918 the British Army had fielded 70 divisions).
There's a puzzle here I've never seen resolved - the manpower strength of the British Army continued to grow even as the front-line forces declined , exceeding 2.5 million in 1945. 25 divisions from 2.5 million men is a tail-to-teeth ratio that exceeds even the US (who managed 91 divisions on a peak strength of 8.2 million men) , yet contemporary accounts insist it was impossible to keep up with the demand for replacements.
More to the point, what's likely to affect the Victor isn't the manpower squeeze but the resources/production squeeze. By mid-war, the British are short of raw materials, refined metals, machine tools, skilled manpower, fuel and pretty much everything else. They're not the US, with Detroit's vast machine-tool industry, nor the Soviets who can devote entire cities to tank production, and they have far more competing priorities than they can hope to meet. I'd expect tank production to be de-prioritised in 1942 assuming the North Africa campaign wraps up - the air defence of the UK is still priority #1, the Navy needs every escort it can get to fight the U-Boats and the bomber offensive is incredibly resource-intensive,
When the time comes to build the Victor, US production will be ramping up, and the question won't be "is it a good tank?" or even "is it a better tank than the M4?" but "is it sufficiently better than the Shermans that the Americans are handing out like candy to be worth transferring production resources from other priorities?" It won't even be a question of saving hard currency by "building British" because if they decide to build 15,000 Victors they'll have to Lend-Lease more of something else.
[One slight wriggle that might just throw things off - suppose Tripoli falls in autumn 1941 and the British (as suggested upthread) transfer a couple of veteran Australian divisions and an armoured brigade to Malaya to deter the Japanese while they work out what to do next. The IJA observes the transfer and notes that its plans for the Southern Resource Area have just slipped from "high-stakes gamble" to "suicidal lunacy". No Pearl Harbour, no Detroit Tank Arsenal, no flood of Shermans - if US entry into the war is delayed until mid-1942 the British Army might just have to take a much bigger role in the fighting in Europe.]