The recording of suspect's statements has started since I retired so I have no direct knowledge but I have found this:
'If the suspect raises objections to the interview being visual y recorded either at the
outset or during the interview or during a break in the interview, the interviewer shal
explain the fact that the interview is being visual y recorded and that the provisions
of this code require that the suspect’s objections shal be recorded on the visual
recording. When any objections have been visual y recorded or the suspect has
refused to have their objections recorded, the interviewer shall say that they are turning
off the recording equipment, give their reasons and turn it off. If a separate audio
recording is being maintained, the officer shal ask the person to record the reasons
for refusing to agree to visual recording of the interview. Paragraph 4.8 of Code E will
apply if the person objects to audio recording of the interview. The officer shal then
make a written record of the interview. If the interviewer reasonably considers they
may proceed to question the suspect with the visual recording stil on, the interviewer
may do so. See Note 4G.'
Thats from:
https://www.whatdotheyknow.com/request/52919/response/132216/attach/html/5/PACE%20Code%20F%20Visual%20recording%20of%20suspect%20interviews.pdf.html
If you are a witness the officer in the case may, for whatever reason, consider that you are a 'vulnerable person' and may wish to video your evidence to produce in court. If that is the case you can refuse.
Things have moved on a lot since I was interviewing people...