What are the ten most populated cities in Britain?

Depends what measures you use. I prefer real urban areas rather than council boundaries which can be arbitrary. These are approximate populations of the 'top ten'

London - 8m

Birmingham 1.8m

Manchester 1.6m

Glasgow 1.1m

Newcastle 800,000 (Tyneside incl Gateshead)

Leeds 620,000

Liverpool 580,000

Sheffield 540,000

Edinburgh 460,000

Bristol 440,000