Bugging is standard in UK prisons
I don't know why this bugging issue has come as such a shock to everyone. It was common knowledge whilst I was in prison that the visit room was bugged. This is why any sensitive information was exchanged in the form of handwritten notes with the visitor, to avoid the authorities gaining an unfair advantage from having access to my intended legal action.
This interference in communication with those outside the prison was not limited to the visit room. A sequence of several of my solicitor's privileged letters went missing at a critical point in my legal case. Letters to Members of Parliament were not considered "priviliged" and had to be passed unsealed for reading by the prison censor. So any thought that a prisoner could have private correspondence with their MP went right out of the window.
My MP Andrew Mackinlay visited me on two occasions at HMP Full Sutton, and we discussed many issues about sensitive aspects of my conviction for espionage, for which I was serving a sentence of 20 years. It is interesting that shortly after one of these meetings, and following some parliamentary questions by Mr Mackinlay, his home in Tilbury was burgled, and Mr Mackinlay was of the opinion that the Security Service were implicated in this - you can see his cryptic comment in Hansard for 26 October 1999.