(ii) in the case of a pilot's licence, to act as pilot of any aircraft flying in controlled airspace in circumstances requiring compliance with the Instrument Flight Rules or to give any instruction in flying;
The ANO as quoted in post #2 by mmflynn states no IFR in CAS, so if the Canadian PPL includes night flying privileges, then the OP can fly in the UK at night outside CAS while IFR, or inside a CTR if he gets a SVFR clearance rather than an IFR one.