Cheers, Mac.
It seems no costs at all. Around half of British constabularies use an uploading service and promote cyclists to load evidence. Apparently more are going to. The service was launched in mid 2018.
The standards of evidence can be low, typically from wide angle lenses that obviously give distortions and with no uniform mounting criteria. Prosecutors (police) seem not to have been given training in understanding distortions or (which I find criminal) use of reference points to judge distances.
There are different requirements between forces, from no analysis of cyclist behaviour through to the cyclist having to submit 4 minutes of footage so that their behaviour can be assessed (and charged if appropriate).
It seems that there is a national police conference in March this year to try and establish more normalised procedures.