That's what I said. The bit outside UK airspace is done on a VFR plan, under VFR rules (and conforming to any local rules wrt. NVFR). The bit inside UK airspace is done under IFR, on an IFR plan, but maintainng VMC.
One way that means a 'Y' flight plan, the other way a 'Z' flight plan, with the change of rulesets at the FIR boundary.