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