With all these apparent anomalies and queries I'm not sure I would progress with this.
Does it have massive advantages that outweigh these?
Are you buying or leasing?
I wouldn't buy ir personally
If leasing make sure you have an exit strategy if you decide to go ahead
I see the
possible drawbacks in a completely different light. They are a chance to bargain and to get something that appeals to you at the right price. I find that as you go through life there are all sorts of opportunities presented. Some people can only see the drawbacks so walk away and then regret it when they see what someone more positive has made of the opportunity. Others see the opportunity while still considering potential problems, and after weighing up the pros and cons decide to give it a go anyway. I'm one of the latter. I have bought several amazing bits of land that had been written off by others with no vision.
I've been told I paid over the odds for a piece of contaminated land. It wasn't as it happened, but nobody had researched it properly. I sold it on for 3x what I paid for it.
I bought 8 acres of scrub land at auction for 2x the guide price. My son asked me what I saw in it. I said I just knew it had potential. As grazing land, because it's sandy the grass burns off in a dry summer. But in a wet summer it's great and it's somewhere where I can now winter my cattle without it getting boggy, and I save a fortune on straw for bedding. But best of all, and unexpectantly, we found out that a one acre compound it has has planning permission for industrial use. We've put some units on to let out and get far more income from that 1 acre than the rest of the farm together.
So basically what I'm saying swuk is that you need to weigh up the pros and cons and what it's worth to you. Consider the worst that can go wrong and take that into account but remember - it might not happen.
As far as the agricultural land is concerned, I don't fully understand why this is a problem although I do know the difference between agricultural land and garden. As it is already being mown as a lawn then I would assume that because you have seen the deeds that you are likely to be the only people that know (or care) that it is technically agricultural. If you were to carry on treating it as garden for 4 years then you can apply for a certificate of lawfulness to have it included in your curtilage. It would only be a problem if anyone complained - and why would they? I myself bought an extra quarter of an acre of land to add to my garden. I have used it as garden for the last 25 years although technically it's agricultural. But no one is bothered because it affects no one else.
I personally would go for it. What's the worst that could happen?