Couldn't they? Letters are cheap to send. They could simply send out a few million or so letters, maybe costing a million £ or so. Offer everyone a settlement

Couldn't they? Letters are cheap to send. They could simply send out a few million or so letters, maybe costing a million £ or so. Offer everyone a settlement of a few hundred £ to cover all past transgressions with the threat of suing for a much greater sum if there is a repeat offence or if they do not comply. If you work on the basis that about 50% just pay up straight away that's quite a lot of money. This money can be used to subsidize going thermonuclear on at least a few thousand of those who don't. Besides, they don't need to sue everyone to make people scared enough to avoid pirate sites.