Well it doesn't look like anything's going to happen about the breach of covenant. That's obviously been going on for decades with no action being taken.
As for the possible contamination - again there's plenty advice on the internet about what you can do to mitigate it. Only you can decide whether to take it or leave it.
However, for what you want the land for, I would possibly be more interested in where the nearest water and electricity supply would come from. You can't rely on running a market garden with rain water alone, and although you can use solar or generator power, a mains electricity supply would be much more convenient and lack of it could limit your future plans.
I have recently developed a green field site with absolutely no services and you would not believe how much it can cost to get things connected.