I'm not aware that there's any way for the various government agency's to find out if you do own a smallish bit of land, unless you were either in receipt of grants for it or making sufficient income from it that it has a mention in tax returns. From a moral point of view, if it keeps you fit and happy and you aren't getting income from it, why should it be taken into account at all? I'd be tempted to accidentally forget to mention it (Crohn's disease is awful, my sympathies- I think 'Dynamo' also has it, but isn't one of the symptoms acute forgetfulness? ).
My 'pension fund / savings' consists of various tangible physical assets. They give me pleasure, appreciate steadily and are not officially recorded or subject to any regulation. If I need money, I can sell one. If I have spare, I buy another. What they are worth and have many I have is known only to me, and I consider them 'property', not cash or a declarable investment. It also means if any financial institutions go t*ts up, we don't have a repeat of losing our savings. - We did have a substantial number of RBS shares which lost 99% of their value virtually overnight. As the years pass by I increasingly have zero trust in governments and financial institutions and think we are largely on our own.