Comment by panarky

There have been reports going back to the Echelon days that the NSA and GCHQ collaborate to evade each nation's laws.

The ideas is that US agencies supply the UK with technology and training, the UK collects sigint in the US with US knowledge, then shares intelligence with US agencies.

The US reciprocates by spying on UK citizens and sharing the intelligence with UK agencies.

That way US agencies can say they don't spy on innocent Americans on US soil. But it's just another elaborate deception.