I didn't realise that there are so many. Most are quite easily recognisable with a basic knowledge of Welsh orthography...but some aren't. I was hoping Doncaster might have an official Welsh name but I couldn't find it...I reckon it ought to be 'Caerdyn' though.
Here's the list:
Bath - Caerfaddon
Bristol - Bryste/Caerodor
Cambridge - Caergrawnt
Canterbury - Caergaint
Carlisle - Caerliwelydd
Chester - Caerllion-ar-Dyfrdwy
Gloucester - Caerloyw
Leicester - Caerlyr
London - Llundain
Liverpool - Lerpwl
Manchester - Manceinion
Oxford - Rhydychen
Shrewsbury - Amwythig
Winchester - Caerwynt
Worcester - Caerwrangon
York - Caersfrog/Efrog
Chichester - Caerfuddai
Crewe - Criw
Exeter - Caerwysg
Hereford - Henfford
Lancaster - Caerhirfryn
Leominster - Llanlleini
Ludlow - Llwydlo
Penrith - Penrhudd
St. Helen's - Sain Helen
Salisbury - Caersallog
Catterick - Catraeth
In wonder why there are so many with Welsh names. Some of them look great, but pronouncing them is another matter. I always have trouble with the double 'll' sound.