In the US, part of their response to prison conditions and over-crowding is a widespread use of GPS and similar trackers. I don't know what the set-up is in the UK but it's common for people in the US (on remand or as part of probation) to have to pay for their tracker services (it's expensive). People have to notify a hotline if they go anywhere outside their agreed routes (e.g., work, to visit the doctor, see family etc.).
The exception seems to be those prisoners on remand who've not yet been charged. They can be released on bond after a set number of days is exceeded (that is a disgrace to be held for so long but it's a separate issue) and they tend not to be charged for their ankle monitors, trackers etc.
Long way to say, let's not overlook the potential of e-carceration. I'd strongly oppose it but I'd at least like this society to consider more options before shrugging off this harmful issue. I'm saying this while knowing that there's no way to stop online access for most adults so it wouldn't make a difference but at least let's discuss some sort of penalty or remedial education.