Erm....not all ISPs have to be in on it...
When it comes down to it Global Area Network (GAN) links that carry the traffic between continents and the such like aren't that many and tapping into these is not beyond the abilities of governments.

Also in terms of the ISPs you only have to get the REALLY big ones to agree to catch the majority of traffic, and in the case of like BT here, a lot of the smaller ISPs end up routing over BT's network to a degree anyway, so you would catch them that way.

There was a case on something similar in the States, and as much as I hate to link to Suckipedia, it was the quickest reference I could find:

en.wikipedia.org/wiki/Hepting_v._AT%26T
(repooc, Wed 7 Dec 2011, 13:53, 1 reply)

I don't see the difference.
You're still talking about a lot of people being involved.

And even then, you're not catching all of it.
(username failed moderation, Wed 7 Dec 2011, 14:25, closed)

It doesn't require a lot of people to do this sort of thing, outside the organization that's doing it....
That's kinda the point....I think you'd be surprised how few you can actually set this sort of thing up with.
(repooc, Wed 7 Dec 2011, 14:30, closed)

No I wouldn't
more than would ever keep it secret.
(username failed moderation, Wed 7 Dec 2011, 14:31, closed)

Who said it's secret?
Gaz me if you'd like to discuss, to save everyone else on this thread, it's simpler than you think....

But also, this sort of stuff isn't being kept secret very well either.
(repooc, Wed 7 Dec 2011, 14:35, closed)