France did but Britain largely did not upgrade the ROW to be straighter.

And it's largely irrelevant anyways because true high speed rail (TGV, HS2, ICE) doesn't start showing up in Europe until the '80s, long after WWII reconstruction wrapped up.

The UK has several “mainlines”, all built before WW2. All are fairly straight and have been smoothed and updated continuously since WW2. Anything destroyed in WW2 was repaired as quickly as possible at the time. Britain didn’t really “make use” of bomb damage to change the layout of London as it wasn’t really destroyed.

And then in the 1960s Dr Beeching’s cuts closed almost half the rail network.

The only new high speed railway in the UK opened in the 90s to connect London with the continent, I.e. Eurostar

Most damage was to nodes not to the links between them. So important junctions were rationised but routes weren’t realigned.