I am amazed how many people are surprised by this. There have been several threads on mumsnet about this over the last few years.
The proposals stem originally from the Tower Hamlets Mayoral Election of 2014 where voter fraud (both in person and postal) was massive, and along with other rule breaking resulted in the whole election being declared void.
Voter ID was trialled in 5 areas in 2018 and in a further 10 in 2019 to test how it worked and what delays and problems may have cropped up, so that the national launch in 2023 used best practice.
It is estimated that 92.5% of the electorate already have suitable ID.
There was no evidence of reduced turnout when the ID requirement was introduced in N. Ireland (although N.I. usually has lower turnout than the rest of UK anyway)
Regarding an ID requirement blocking people from voting, what is the current excuse? In the 2019 General Election, there were 287 constituencies in which turnout was less than two-thirds of the electorate with Hull East being the lowest at 49.3%.
Proven cases of voter fraud are low, but suspected cases are significant. Talk to people who work in polling stations and they will tell of one person turning up with 6 voting cards expecting to be given 6 ballot papers. I have heard of a person handing in a voting card who they were sure had already voted earlier, but there is nothing they could do about it (especially when they voluntarily showed supporting ID for the suspected second vote). They may have observed a "leader" of some sort directing "followers" exactly where to put their crosses. They may have seen cases of people voting with an apparently legitimate polling card who they suspect lives in a neighbouring borough and may also have voted there.
The rules for postal votes are also due to be tightened, but it was left out of this Voter ID legislation - it may come later. Proposals include needing to re-apply every 3 years for a postal vote, tightening up ID checks, introducing online applications, and much tighter restrictions on who can hand in postal votes at polling stations (where it is too late to post the ballot paper).
Although people without ID will not be allowed to vote, I have yet to hear what will happen if the ID presented is "questionable". In some countries the person is allowed to vote but their vote is "quarantined" and put to one side when the other votes are counted. If the number of quarantined votes is less than the majority, then they are discarded.