Despite all the warnings the government is determined to press ahead with its decision to close the existing electoral roll on December 1. This red letter day in British politics is no cause for celebration. As the Smith Institute’s latest report on the switch to the new system of voter registration shows, we are about to dramatically shrink our democracy. As many as 10 million people are likely to vanish from the electoral register for ever – equal to 20 per cent of the total electorate and greater than Labour’s entire vote in the 2015 general election.

Anyone who has not transferred over to the new individual electoral registration system by next Tuesday will be “dropped off” the register. The independent Electoral Commission, mindful of how the loss of voters will play out in forthcoming elections, say they need at least another year to ensure the new accuracy and completeness of the registers.

Nearly half a million voters (mostly the young and those in private rented homes) will disappear from the London register. According to a recent HeraldScotland survey around 100,000 residents in Glasgow may also be left off the new system. The picture is likely to be much the same in other cities, especially in places where there’s greater mobility and concentrations of students.

These depleted registers across the UK will impact more on marginal Labour seats, especially where turnout is already low. Conversely, they will benefit Tories in future local, Euro and general elections. As the Smith Institute report observers, Conservative voters tend to be older, home owners and less transient – and therefore more likely to appear on the electoral register.

The government continues to ignore the prospect of skewed election results owing to an incomplete electoral registers. The attitude of some Tory MPs hardly helping. For example, Eleanor Laing MP (the former shadow minister for justice) told the BBC that “if a young person cannot organize the filling in of a form that registers them to vote, they don’t deserve the right to vote”. Leaving aside such glib remarks, what we do know is the new registers will tend to favour MPs whose support is found in more affluent rural and semi-rural areas which have stable populations.

Even more worrying, the forthcoming changes to MPs constituencies (under the Boundary Review) will be based on the new electoral register. The new parliamentary constituencies will be based not on the voting population, but on an inaccurate and incomplete register. As Institute’s report argues, these changes are likely to unjustly benefit UKIP and the Conservative party.

That’s not to say that the voter registration system doesn’t need reforming. It clearly does. Indeed, every evidence-based analysis of electoral registers over the last 20 years shows that both accuracy and completeness are declining – the two features of any electoral register that make it credible or not. But, the job must be done properly. Casually leaving 10m voters off the electoral resister hardly suggests every effort has been made.

The legitimacy of our democratic system rests on ensuring that everyone can exercise their right to vote. This is a task which shouldn’t brook complacency or compromise. We should be aiming for maximum voter registration, not settling for a system where one in five drop off the register.