I'm sure Raleighs came with Bluemels mudguards. That was the most popular brand (pun not intended). Here is a good example:

Raleigh Record Ace 1948

It's possible that later on they were branded "Raleigh" since it was such a large manufacturer, same as Schwinn branded outsourced components.

I think celluloid (nitrocellulose) was phased out as a material in the 1950s, except maybe for pingpong balls, because it's so flammable.