Not in Europe?
It's available on Prime Video (at least on amazon.de). For a long while they would only sell access to season 1, but I've just checked now and all 4 seasons are available at the moment.
It does seem to be available on ITVX in the UK.
alt Hacker News
It's available on Prime Video (at least on amazon.de). For a long while they would only sell access to season 1, but I've just checked now and all 4 seasons are available at the moment.