I was reading about this the other night in an old book of my grandfathers. In OTL it took the British a long time to adopt this idea of a squeezebore adapter. The idea itself wasn't new by any stretch of the imagination and Janecek had been in the country since 1938.
I know it's a bit of a stretch but bear with me. Let's say in TTL Janecek's idea gets some political traction pre-war and tests are done in late 38/early 39. These tests go quite well and convince the British of the value of the squeezebore principle especially in regards to the 2pdr anti-tank gun. The decision is made to produce the adapters and make the requisite changes to the ammunition being produced.
I'd imagine that tanks and AT units equipped with these adapters would acquit themselves fairly well in France, though I don't see it being enough to change the outcome of the campaign. My basic idea is that following Dunkirk, the British have a much better Anti-tank weapon in the squeeze bore 2pdr than they did in OTL leading perhaps to better performance in Africa later on?
Then again I suppose a better POD is to have he 6pdr anti-tank gun's development go faster than OTL...