I thought the license fee was a tax. You have to pay it, except in extremely specific scenarios that are basically just the bureaucracy's way of saying it's technically optional even though it isn't. AFAIK you have to own no devices capable of receiving BBC broadcasts - this includes most phones and computers since they broadcast on the internet.
You only need the license if you watch live TV (on any service) or use BBC iPlayer.
If you only watch DVDs, or stream movies etc, you don't need a license
When did they change it from if you could watch to if you actually watch?
Technically the rule never changed. If a licence inspector sees a TV connected to an ariel socket then you're breaking the law.
But there's virtually no inspections any more. There were a lot of bad newspaper headlines about poor single mothers going to prison for getting caught (and refusing to pay the fine, but that bit usually got left out), so enforcement basically ended.
In about 2008 it was OK, my flatmate let the "TV licencing" people in to see a TV connected only to games consoles and a DVD player.