Unhappily this requires a total revolution in the British car industry, given its origins in WW1. We produced some brilliant sports carssuch as Jaguar and MG., but the mass industry was found wanting.
You would have to go back pre-WW1, the Red Flag Act is repealed early, commercial steam wagons start much earlier and a road industry is established.
Then you need some engineering genius, the equivalent of Ford or Daimler to start volume car production before WW1.
By 1945 you have three large companies plus the Independents (the sports car makers) like evrybody else, instead of the six plus producers. Then someone produces the equivalent of the VW. We'll say Tucker flees the US. before he gets prosecuted and signs up to a dealwith the British government and his designs get produced over here (I could do with those swivelling headlights).
Something that looks like the truimph, wings and all, gets produced and sweeps the world.
Since British cars are smaller than US. with smaller engines, they are what many countries in the world want.