I'm actually a Yorkshireman! Just living in Canada temporarily. But I'll still take the compliment
And I always thought it a good rule not to jump in with unsolicited advice but I guess I could throw in my two cents on this subject if I'm now welcome to.
To the OP: I would personally add in some resistance training to your walk. Seeing as this is an outdoor forum I will say that doesn't necessarily mean spending hours inside a gym. I used to for example occasionally use a heavy log in a clearing next to a nice river. if your creative enough you can get a really good workout that way with just a piece of wood and some knowledge (bushcraft style
At first glance walking is a great way to burn fat because it's of the right intensity to keep you in an aerobic training zone, perfect for burning fat. However the problem I have always found with walking is that it just doesn't burn enough calories for the time you're doing it. You generally have to walk for hours and hours to offset a decent diet. And even though your body is constantly burning at least some fat it doesn't really get into full fat burning mode until your bodies carbohydrate stores have been depleted to an extent. The best way to do that is by high intensity stuff like weight training.
So, do 40 minutes of high intensity training and
then go for your walk, that way by the time you start walking you have already depleted a lot of your bodies carb stores and will get a much better fat burn and wont have to walk as far. I also add that of course cutting back on your carb intake in the hours leading up to your walk makes the whole thing much more efficient.
Plus, if your not doing any resistance training and a whole bunch of walking you'l find that you lose muscle as well as fat which slows your metabolism down and makes the whole thing that much harder in the long run.
Don't wanna sound like a mr know it all so I'll leave it at that for now, happy to help the OP or anyone else though should anymore questions arise from my mini essay.
Oh and P.S the High fat high protein inuit style diet I'v found is one of the best for fat burn, perhaps not long term health, but definitely fat burn. Its a great way to keep low insulin levels, which is key to fat loss. And also partly explains why native peoples on this type of diet are prone to diabetes and obesity when introduced to processed carb "modern diets", Their genetics are just not designed to cope with the blood sugar levels