A widely accepted democratic principle is the notion of universal and equal suffrage, expressed popularly as 'one person, one vote'. This principle now seems so absolute, we tend to forget how recently it was realised in the UK, how long and bitter were the struggles that got us there - and how quickly we came to undermine it.
It took until 1928, when the vote was granted to all adult women, for a universal franchise to be achieved in the UK. It took another generation, with the abolition of additional votes for business owners and university graduates in 1949, before the franchise could be described as 'equal'.
To reach this point had taken more than a century and multiple Acts of Parliament - starting with the Great Reform Act of 1832, which extended the franchise to 7 per cent of the adult population. Along the way, campaigners were killed at Peterloo in 1819, 20 Chartists were killed by troops in Newport in 1839, and Emily Davidson died in 1913 after throwing herself in front of the king's horse at the Derby. Countless more radicals, Chartists and Suffragettes were imprisoned for their campaigns to extend the franchise. But finally, in 1950, a general election was fought on universal and equal suffrage.
Or was it? It has long been recognised that our electoral system prevents all votes from counting equally (millions of votes are wasted in 'safe' seats, while a mere 100,000 votes cast in 'marginal' seats determine the outcome of the election). But it is also apparent that our system of voter registration has always led to a significant minority of voters being excluded from the electoral process.
The reasons are partly historical. As the franchise was extended from the Victorian period onwards, we remained reliant on the annual canvass of electors to compile the electoral registers. Carried out every autumn, this has proved reasonably effective in identifying eligible voters and updating the registers in light of population movement. Yet even in the 1950s there was still a core of 4 per cent of voters who were absent from the registers following the canvass. And because the registers were updated only once a year, by the time an election came around many more voters were effectively disenfranchised simply by moving house.
Since then, things have got worse. By 1990, around 8 per cent of eligible voters were completely absent from the registers. Registration levels then took a substantial further hit in the early 1990s, when some 600,000 voters de-registered in an attempt to avoid payment of the poll tax. Margaret Thatcher later claimed this helped the Conservatives win the 1992 election.
There was another big drop in registration levels in the early 2000s. Over half a million voters again disappeared from the registers and, this time, there is little evidence that they have returned. Those missing are most likely to be young people, members of ethnic minorities and residents of safe Labour seats in metropolitan areas.
Meanwhile, around one-tenth of voters continue to lose their right to vote each year because they move home. Younger voters and ethnic minority voters are also most likely to be disenfranchised in this way, since they are more mobile than other social groups. Although voters now have the right to register at other times in the year, few make use of this provision. As things stand, at least 15 per cent of eligible voters will be unable to cast ballots at the 2010 election, with this figure rising to 31 per cent among black and ethnic minority voters and 56 per cent among electors aged 18-24.
An urgent task for the incoming government must be to consider whether our system of electoral registration remains fit for purpose. There is also still time for political parties, electoral administrators, and voters themselves, to take action to improve the situation; voters can register up to 11 working days before the election. While a last-minute registration drive is essential, it may not be especially effective, however. Recent surveys suggest that candidates will do well to persuade two-thirds of registered electors to cast votes in 2010. Getting unregistered voters to the polls will be even more of an uphill struggle.
Stuart Wilks-Heeg is director of Democratic Audit and a lecturer at the University of Liverpool. He was also the lead author of the Electoral Commission's report on the completeness and accuracy of the electoral registers, published on 3 March 2010 and available at www.electoralcommission.org.uk