Counter-terrorist police officers in the UK are taught CQB either by the SAS or by people who were taught by the SAS.
So it's possible these were cops, from anti-terrorist squad or special branch, or maybe security service spooks. It's possible that they were SAS but my guess is that they were cops. There are only a couple of hundred badged troopers in the real SAS, and they're mostly kind of busy elsewhere.
Dumping the guy on the ground hard, sitting on him and putting a clip up his nose is 100% pure SAS style though.
My wife and I have a friend who was Spec Ops for us in Nam. He serves as a consultant to various Swat Teams and probably to our military.
He told us that a lot of the special unit guys for London's police force are former SAS guys, both retired and guys who are out of the military.
He said that they train the London Cops on a regular basis. However, in most cases where a gun is used, the officer was a retired SAS or had served. One of their trade marks is no bad guys live after being shot by them.
Re the regular SASers being busy. He predicted that within hours after 7/7 they were flying to various parts of the world to settle accounts.
I will see him this afternoon and ask him.
Regardless, great job by these brave men. The good citizens of London can be assured when there are men like that protecting them.