A circuit breaker is a lockdown and it is a term that scientific advisors and politicians use so it doesn't look like they are backing "lockdowns" (when actually they are). Yes it was a Sage recommendation, but there is no real proof that a 2 week lockdown in October would've solved all of our problems or brought cases down to the extent where things could open up again. Just conjecture and my opinion, but I honestly think if things had closed for 2 weeks in October, we'd probably have locked down by now again anyway.
Also, Christmas is hardly going to be a 'circuit breaker' because it looks like a lot of the social restrictions will be relaxed. What I was trying to say is they probably have the scope to do this because all the mixings in schools and offices won't be happening because they'll be on holiday anyway. And the problem they'll have is that when everyone is back at work or school after Christmas and they try to re-introduce stricter social restrictions, I think a lot of people, having had a small taste of freedom, won't bother listening.
Hopefully we are not discussing this sort of stuff for too much longer anyway because we can see now that lockdowns are not the solution to the problem and there is a danger of the cure becoming worse than the problem. The solution is mass testing of the population (with rapid results) together with an efficiently rolled out vaccination programme. If these things are starting in December then hopefully we are on track for relative normality by Spring.