This question always causes great debate. It depends on how you measure (area or population) and when you measure (new places granted city status & increases / decreases in boundaries / population).
There are currently 50 cities in England. Lots of information available at this link to the Lord Chancellors Dept :--
http://www.lcd.gov.uk/constitution/city/citygj.htm
#part6
My estimate of the largest English cities, by population, starting with the largest is London, Birmingham, Leeds, Sheffield, Bradford, Liverpool, Manchester, Bristol, Wakefield, Coventry. And in 11th place, Newcastle.