You can have credible evidence about something that is inadmissible in a court of law, or even from a secure source that they do not want to reveal. So yes, MI5 can make claims without having to be held to account for them. I personally am more than happy about that.
So MI5 can get parties to drop candidates just by saying they “could” be a spy, without proof, or conviction?
Literally anyone “could” be a spy.
Doesn’t that mean the spooks can basically veto any candidate they don’t like?
You can have credible evidence about something that is inadmissible in a court of law, or even from a secure source that they do not want to reveal. So yes, MI5 can make claims without having to be held to account for them. I personally am more than happy about that.