There have been 12 by-elections in England and Scotland since the start of the current Parliament - Oldham and Saddleworth, Barnsley Central, Leicester South, Inverclyde, Feltham and Heston, Bradford West, Corby, Manchester Central, Cardiff South and Penarth, Rotherham, Middlesbrough and Croydon North.
BBC: Voting nearing an end in Eastleigh by-election