I don't know where to start!
If you remember, we recently had a scare over BSE. Still do, really. This was due to the rubbish going into feeds. Don't be so quick to assume British feed merchants would not do such things.
4500 Euros seems to me a good price for public access to 50 acres. You have to remember that if all the land was available for roaming, the number of people visiting your bit would not be so great. People moan about footpaths over their land, but they get by.
But you also said plainly that your farm does not and can not pay. It is your hobby. I understand this perfectly. We have a similar hobby farm. Which also does not attract subsidies.
A hobby farm is different to a commercial one. No one is suggesting that people should be allowed to wander in peoples back gardens. It is necessary to define private space. But it is becoming unfair to define private space as 'everything I own'. I think it is also counter-productive. Why should townies subsidise or even understand somewhere they are not even allowed to go?
In the 60s Britain had stiff trade barriers to keep out cheap foreign food, except from 'the colonies'. The price farmers got was kept artificially high compared with world prices. The price in the shops was artificially high.
This was because the governments at the time felt it necessary we produce as much as possible of our own food. In case of world war three. WW2 demonstrated that britain could not feed itself. Food shortages continued after the war, not because of U boats but because we were broke and could not afford to pay. Anyway, governments have abandoned trying to be self-sufficient in food because it costs too much...compared to buying food from abroad. And because WW3 would be over in 2 weeks after all the nukes went off.
The extraordinary thing about the official public attitude to countryside is that no one understands it has to be managed to stay the way it is now. Or to become very different but still look the way it is now.
Planning rules need to be changed to either declare the countryside as park which the government will pay for, or let people there get on with whatever they can do which will bring in some money but still preserve the look and feel of the place.
I think possibly we could feed our population ..just. But absolutely no one is willing to live on a diet of carrots and porridge for the rest of their life if they have a choice. A lot of EU farmers might be in trouble too. The EU also has a policy of keeping out cheap foreign foos. But many other EU countries have better land and climate than we do.
Farm diversification is very popular amongst politicians. But there is a limit to how many golf course you can have before none of them has enough customers to make money. Someone has to tell those idiots in charge that we need rich people living there. Cheap housing. Small businesses. Computer programmers in their purpose built offices. Old car restorers. local furniture makers. Just about anything you can squeeze in.