In the late 1950s- not much different from 1944 as there were still no motorways - a friend and I regularly did Birmingham to Ferndown, not much different to Birmingham to Portsmouth, late at night in a Jaguar in two and a half hours. The same trip in your average saloon car was closer to 4 hours during the daytime.
Some years later, when the A34 was a dual carriageway and I could pickup the M40, I could do it in just over two and a half hours in the daytime in my Audi 200. I doubt if that would be possible now with the much heavier traffic and speed restrictions all over the place, not to mention roadworks!
Maurice