14,000 in the right places could easily topple a government in a tight election because of FPTP - although one can obviously not choose in reality.
In 2017 for example the minimum number of votes across the country needed to take down Theresa May (or more realistically have her form a true minority government) was something like 2500.
We have an extremely disproportional electoral system.
That would have been 2500 in exactly the right places. 2500 in exactly the right places could also have given the Conservative Party even more seats.
If we are talking about 0.25% on average then I doubt it could have changed much in these local elections (back in May in England and Northern Ireland).
If anybody wants to play with the data from the General Election in 2017 they can do so here:
Sort the table by "Mjrty." in ascending order. Right at the top we see wins for SNP, Labour, SNP, Labour, and Labour that easily could have been wins for Lib Dem, Tories, Tories, Tories, and Tories.
This article says that 70% of them just didn't bring any ID with them. That's on them.
It also says nothing about the remaining 30% except that they "brough a type that was not accepted". We don't actually know if they even had the right to vote.
Though since the correct ID is basically every kind of ID that's valid to buy age restricted goods like alcohol and stores have become more and more strict at checking that over the last few years that mostly seems to have been older people. (The government also permitted some other kinds of ID that older people are more likely to have access to in order to reduce this, but it didn't completely eliminate the problem and I'm pretty sure it wasn't expected to either.)
The press has, as usual, not been entirely honest about this. In particular, there was a talking point about how only one non-passport and non-driving license form of ID that young people are likely to have compared with much more forms of ID that older people will have, but that one form of ID is a blanket scheme that providers of ID sign up to in order for it to be valid as proof of age. There is no equivalent blanket scheme for ID that older people are likely to have.
During the recent elections in England about 14,000 people were denied a vote due to lack of ID.
https://www.bbc.com/news/uk-politics-65988959