• England:
  There are 3,127 maintained secondary schools, with 3,055,460 pupils, in England. Information at Local Authority level (tables 10) is available on the DfE website. 
• Northern Ireland:
  There are 219 maintained secondary schools in NI with 147,759 pupils 
• Scotland:
  there are 301,017 pupils in 372 secondary schools. 
• Wales:
  There are 223 maintained secondary schools in Wales with 203,907 pupils. 

Data sources:

• England: Schools, Pupils and Their Characteristics: January 2010 (updated in June 2010).
• Northern Ireland: Northern Ireland Department of Education.
• Scotland: Summary statistics for schools in Scotland, 2010 edition.
• Wales: School Census, 2010.