This is an interesting post.
A lot of information in the public domain about this issue currently seems to be due to emails that were sent and to me the revelations that are currently driving public opinion are largely due to the extra emails that have recently been uncovered.
To me this represents something of a catch 22 situation. If the government didn't know that these emails existed then people are going to argue the vetting process was not strong enough.
If the government did know about these emails, then surely it is an admission of the level of monitoring the government undertakes on certain individuals, and the question then becomes whether this level of monitoring is appropriate.
Then of course there is all the other information that the vetting process might reveal about an individual, and the possibility that revealing this information may not only reveal further information about the issue, but also on information gathering techniques and maybe even raise greater public awareness of how the government gathers information and whether this whole process is appropriate.
So the debate to me risks spiraling into not only a question about one individual, but about how the government monitors citizens in general.
If I've got this right then it presents a significant headache for the government on how to handle it, both in terms of allowing transparency (if the government are not transparent then everyone will cry "cover up") and in drawing unwanted public attention to just what the security services are doing and the information they collect (security services generally want as little public attention as possible).
Would Starmer falling on his sword now draw public attention away from the details here ? I am not sure.