Why is it SRU?

[Killjoy]

Yeah it's from Flashpoint.

Not sure if that was a coincidence or whoever renamed it (termin I think?) actually meant that.

That would've been me. 
When we implemented a tactical unit for the police forces, we didn't want to go with SWAT as that's too unoriginal. Fallen wanted it to sound more British and titled it Special Services, or SS, which was later often mistaken for Secret Service. 
I reformed the unit to SRU, indeed motivated by the TV show Flashpoint and issued the rules forbidding SRU to serve as the President's personal security (a huge problem during SS times.)