You're welcome Dominic, i've achieved similar figures from mine on longer runs, for example a trip last year to the Kinson area of Bournemouth for a friend to collect a car he bought on ebay returned 31mpg. I should add mine is on LPG so the general multiplier to get the "correct" petrol consumption is 1.3 so arguably i would have returned ~40mpg on petrol.
Knowing the roads you mention and roughly what i get around here on similar roads (but without the hills) i generally get 27mpg which works out ~35mpg when "corrected". Where possible, on unrestricted roads, i try to keep my speed at an indicated 78-80mph which is (by GPS) a real 73-75mph as i've found this gives the best economy on a longer run, ~2500rpm so the engine is just into the power band properly.
Talking of winter motoring, i had a nasty scare last year when i encountered some ice and nearly got intimate with a telegraph pole. Since fitted a new set of tyres as the ones on there were all 10+ years old and had obviously gone hard, despite having good tread. At the time my other car was a Volvo 760 GLE on near new cheap tyres and that had gone round the same junction without even a twitch hence pointing to the tyres being the cause of the problem. If your tyres aren't reasonably new, it would be worth double checking them before winter in the light of this. 😉 😄