The polls have opened in two constituencies in which by-elections are taking place following the deaths of the sitting MPs.
The by-election in the safe Conservative seat of Bromley and Chislehurst was prompted by the death from cancer of Eric Forth, 61, in May.
In Blaeneau Gwent, Peter Law, a 58-year-old independent MP and member of the Welsh Assembly, died in April following a year-long battle with a brain tumour.
In both cases the period following their deaths has not been without controversy.
Conservative activists in Bromley and Chislehurst rejected David Cameron's attempts to modernise the party, by snubbing an 'A-list' of MPs in waiting.
The local association instead opted for London Assembly member Bob Neill, 53, over Mr Cameron's preferred candidates, and the Tory leader has largely kept away from the by-election campaign.
In Wales, controversy followed Mr Law's death when his widow claimed that her husband - a long standing Labour party member - was offered a peerage not to stand against Labour at the 2005 general election.
The claims - denied by Labour - arose from Mr Law's decision to stand as an independent candidate in the Blaeneau Gwent seat, which he won by a huge majority, in protest at the party's use of all-women shortlists in the constituency.
Mrs Law is standing for the Welsh Assembly seat in the constituency. The failure of Labour to take back this and the Westminster seat will be seen as a major embarrassment.
The full list of candidates is as follows:
Bromely and Chiselhurst
Abbots, Ben (Liberal Democrats)
Belsey, Anne (Money Reform Party)
Cartwright, John (Monster Raving Loony Party)
Farage, Nigel (UK Independence Party)
Garrett, Ann (Green)
Hadziannis, Nick (Independent)
Hemming-Clarke, John (Independent)
Neill, Bob (Conservative)
Reeves, Rachel (Labour)
Uncles, Steven (English Democrats)
Winnet, Paul (National Front)
Blaenau Gwent - Westminster seat
Davies, Dai (Independent)
Hope, Alan (Official Monster Raving Loony)
Kitcher, Amy (Liberal Democrats)
Lewis, Steffan (Plaid Cymru)
Smith, Owen (Labour)
Williams, Magrit (Conservatives)
Blaenau Gwent - Welsh Assembly seat
Bard, Stave (Liberal Democrat)
Burns, John (Conservative)
Hopkins, John (Labour)
Law, Trish (Independent)
Matthews, John (Green)
Price, John (Plaid Cyrmu)