Hi Ben, firstly good luck, I hope you do well! Now here's the but. As you know and others have noted, you need to lose weight and only diet is going to do that. You are going to have to make some tough choices if you want to achieve your goal in 9 months as you not only have the weight to lose but also to get fit. Work on your basic fitness level first with plenty of low impact exercise to avoid injury whilst you diet to lose the weight. I estimate you need to lose about 4 stone and each pound lost equals a 3500 calorie deficit so I'm sure you can appreciate the task ahead of you. Plus as you lose weight you'll need fewer calories to maintain weight (as you'll burn less having less bulk to move) so you will plateau and have to cut even more calories out to maintain the loss. I'm not being negative and saying you can't do it, just pointing out the possible issues. I'd suggest cutting out all alcohol and focus on good quality lean meat and fish with plenty of fresh veg. Cut right back on spuds, pasta, rice etc. I like to make big tasty veg based meals like chilli and substitute the mince with lentils, a very healthy source of protein, lots of veg in it too like carrots, peppers, aubergine, green beans and anything else you like. Don't eat any ready meals or bought sauces as they have too much sugar and fat in them. You can cook any onions for the base of your meals in a little water but if you have to use oil get yourself a bottle of spray oil. Homemade soups are also a great way to go, tasty, nutritious and low calorie if you are careful. So again, good luck, don't push too hard as being injured definitely won't help!
Chris - you are eating more. To gain 4lbs over 12 weeks works out to an excess of calories of just 160 per day which could very easily be slipped in without noticing. You'll just have to work out a way of trimming a few off each day. Also probably answers why you have more energy, not the diet, just more food!
Dr Rob, that truly is bad news but hats off to you for keeping it going as long as you have! This remains my one and only marathon, run(!) on it's first outing. I've not been well for a few years now but always had it in my mind that if I did manage to get back to running then to re-run the Greensands would be my goal. It's such a beautiful route, completely at odds with the brutality of finishing it! I shall just have to think about the Picnic instead although that just makes me want to stay on my sofa!!
That's more like it, as Millsy suggested why not post your exercise/running routine and I'm sure all the helpful people on here will help you with tips as to how to improve. If you do it right, you will definitely improve. Some recent race times would help too.