OS in or out of London?
I think not.
What you may be thinking of is the Company's application to the US Regulator to fly into the US from "any country" in the EU and yes, as written that includes the UK.
However, Sch K means that any flying of that size aircraft in the UK (or any flying at all into or out of LHR or LGW) must fall within the BA / BALPA Scope agreement and put the pilots onto the master seniority list.
BA has never sought to avoid this obligation so won't be taking O/S into London or the UK