cold starts arent the only thing that affects economy in the winter - the denser air requires the ECU to inject more fuel to keep the same fuel/air ratio. The result is worse economy but (theoretically) slightly more power!
also the engine loses more parasitic energy in the form of heat loss - it becomes less thermally efficient. however the increased AC drain in the summer often offsets at least part of the warmer seasonal benefits.
but for this journey it was a cold start, car had been still in the office carpark since 8am lol
