I wondered if it was just the general inexactitude of old maps, but thought I'd mention it just in case!

I think you've got all the main UK cities, but some other possibilities are Norwich, which was quite an important city historically ... and would conveniently fill out the empty space to the east of Birmingham. There's also Oxford and Cambridge, which have had important universities forever, but I'm not sure if that fits with the theme? There's also Swansea, just along the coast from Cardiff, which is the 'second city' of Wales. There's also Portsmouth on the south coast of England. It's been an important port and naval base for a long, long time (It gets mentioned in Jane Austen novels, so that shows how long it's been around!)

Hope this helps.