The Centurion was a development of the British experience with the Comet and Cromwell tanks' deficincies when facing the Panther. Armour historian Simon Dunstan once went so far as to say that the Centurion was built "to counter the Panther."
If there's no WWII, the Centurion may well not be built. Also, the British went away from their misguided "cruiser, etc." tank philosophy after WWII.
Until the mid-50s, there wasn't what we know of today as a Main Battle Tank. There were only Infantry Tanks, Cruiser tanks, etc. The entire doctrine of armoured warfare was changed between the late 30s and 1945.
In Normandy, Canadian troops moving inland kept up with their armoured units by using Priest self-propelled guns with the howitzers taken out as proto-APCs, almost like M113s without a top. This was, too many tacticians, the beginning of the mechanized offensive: the infantry was able to mount up on a vehicle which had at least nearly the same armour as the tanks it was keeping up with.
With no WWII and thus no Normandy, the Canadian army would have no armoured corps, and no tanks at all.
Also, up to and during the Second World War, the British used guns measured by the size of the round: 17 pdr and 20 pdr. It wasn't until afterwards that they switched to a metric system of measurement, such as the L7 105mm and the L22 120mm. Lord knows how long it would take them to stop that.