The SRR is a Tier 1 special forces regiment like the SAS and SBS. They draw from other special forces and the wider UK military, RMs, Paras, etc. They're basically 14 Int. rebranded to my understanding. Yeah they specialise in intelligence gathering and counter terrorism, freeing the SAS to specialise in direct action but are trained by the SAS to do exactly that I believe. That's why they work alongside MI5, CO19 etc with this stuff, they are a military unit designed with a similar objective.
Anyway, the only reason I mention all this is in defence of our security services. Didn't mean to