The number of people turned away at polling stations because they do not have Voter ID will never be known, the elections watchdog has admitted.
People will be required to show photographic ID for the first time at polling stations on Thursday.
But the Electoral Commission has admitted it will “not be possible to accurately quantify” the impact of the new rules by counting who does or doesn’t have ID at the ballot box.
A senior Labour MP savaged the commission’s response, as he questioned how the Government will “learn vital lessons for future elections, when the data is inaccurate”.
Clive Betts, chair of the Levelling Up, Housing and Communities Committee, said: “The Electoral Commission has confirmed that we simply won’t know how many people will have been turned away in a queue outside a polling station because they do not have the requisite ID.
“It appears that the Government has designed a system which denies the prospect of sensible and co-ordinated information collection and makes it almost impossible to judge the true impact of the introduction of voter ID.”
He added: “The Minister has confirmed that the data collected by the Electoral Commission will represent a significant part of the government’s evaluation of the implementation and impact of voter ID.
“The Government, having introduced the voter ID policy, needs to look again and properly recognise the importance of assessing and understanding the impact of these regulations.”
The Electoral Commission intends to record the number of people who are refused a ballot paper by polling station staff because they lack ID, but not if they are turned away after speaking to the greeters that some local authorities plan to deploy outside polling stations.
Its reasons for being unable to count who is turned away by greeters include staff changing throughout the day in polling stations.
There are also difficulties related to people accompanying friends or family at polling stations where they are not registered, it said.
Likewise it claimed voters “could turn around before or after they have spoken” to staff greeting them.
The commission, which set out its explanation in a letter to Mr Betts after he raised an urgent question on the issue in the Commons, also said tracking voters who return after having been turned away earlier “would also be extremely difficult”.
It added that it will conduct polling to assess the impact of the changes.
Critics of the Voter ID policy have said it could result in large numbers of people being unable to vote, with about two million UK voters thought not to possess the correct form of ID, while just 85,000 have applied for a free ID document.
Rebecca Baker, an academic at the University of Exeter and an expert in democratic decline, said: "It is apparent that not enough voters are aware of the change or have sufficient access to trusted information to feel secure in the options available in relation to gaining the required ID.
"The Government has recognised this knowledge would be vital, and without it, the risk of this rollout impeding the voting process rather than 'safeguarding' it, is high."
On April 27, levelling up minister Rachel Maclean told the Commons the policy was necessary for "maintaining the British public's trust in the sanctity of the ballot box" and the Government was "very concerned to get the process of data collection right".
Ms Maclean said data would be collected at polling stations and through a "voter identification evaluation form".
The Daily Mirror launched its Get ID, Get a Vote campaign to raise awareness that the rules have changed.
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