Rosie.....you are 85 years of age....clearly like your food.....so WHY diet. It might, just might relive the pain in your knees and it might just might give you an extra few weeks on you life.
If it is worth it to you....then do it..diet, but if you enjoy your food, then don't restrict your food and fluid intake (wine) for the pleasure that it will give.
You are on a blood thinner Warfarin...too much and you will bleed, too little and your blood will thicken....your INR measurements will regulate this for you.
I have no idea why you should consult your GP before dieting, if you are taking Warfarin.