Well I'm not convinced, but just for the record, you have very little idea of what your are proposing to take on. Others have said the same thing to you, and I will just repeat it. You cannot do what you are proposing to do.
I am a skilled survivor. In the past half a century I have spent anything from a few days to a few years living in temporary shelters, so I know what I am talking about. I could not safely do what you are proposing to do. I would probably die. You would almost certainly die. Something similar might be possible, but not what you are proposing, and not with the amount of experience that you have and the little preparation that you have made and/or are planning to make.
What you have proposed is not legal in the UK. I very much doubt that you know what it legal and what is not legal.
For an example, dumping your sewage in a wheelie-bin is illegal. The fact that planning permission has been granted to an owner of a property to build a dwelling on that property may under some circumstances give the owner the right to dwell on the property in a temporary structure while the dwelling is under construction, but it certainly does not give you the right to move in and set up a semi-permanent camp there, even if the owner supposedly gives his permission. The owner cannot change the planning (and many other) regulations to suit himself nor to suit you. It just doesn't work like that.
There has to be another way, one which does not take such risks with your health and safety.
Put some more thought into it.
I agree with what everyone is saying about food, I will need to have enough basics incase I cant catch anything or find any wild foods. I forgot to state though that this will be part of my research in the following weeks, to find out more about the area. I already know quite abit as im moving there. Permission has been given like you say for a non permanent structure whilst building, building should start taking place in a couple of months.
As I said that was an error, the thing is I already know what I mean inside my head, I have problems sometimes putting everything into words for other people to understand and its not until I read back over it that I realise or if it is read a certain way it sounds wrong , like the wheelie bin thing.
I've slept outdoors with no shelter, walked around in barefeet in winter, im not saying im indestructable but I do alot of things other people pull faces at. As a child I would take the dogs and walk over farmland for good few miles, I ended up in a ditch a couple of times that had muddy sliding banks, I just tied ropes around my middle and got the dogs to pull me out.
Obviously alot of situations you will die in, but i do believe alot of it is down to mental attitude. Im not going to go on 20mile hikes and walk over boggy land or jumping over crevices, that is what I would personally call risky if you are on your own and you do that type of thing.
I would go and get help if anything happened, like I said there is a post office, quite a few houses, a bus. Even if nobody was there right away I wouldnt have to wait long for another person to be within shouting range.
I will make my shelter windproof, I live in a windy area and have to have the chicken runs and greenhouses all tied or anchored down. I will either get some sandbags, turf etc to make the area more sheltered.
I would take food for the dog!! All of the animals would be looked after and well cared for, I have had chickens in the past so understand the ins and outs of chickens. No foxes have been seen in the area but I always keep outdoor animals in housing that is fox proof, the only predators would be birds of prey, possibly mink ,pine martens and then the usuals.