Matrix,
You are pretty much correct,
150 hours total time to start the CPL. The 100 hours p1 is for license issue, so for example if you have 150 hour total but only 95 p1 you can still commence the CPL training.
200 hours total of which 100 needs to be pic for licence issue.
However if you are doing the IR straight after the CPL then you can use the flight time on the IR course to take you over the 200 hour mark; also it is cheaper to submit your IR and CPL application at the same time to the CAA than if you submit the CPL and IR applications separately.