I've found out a bit about the boat owners. Apparently, they had stopped paying mooring fees and are now living in London. They knew the boat was in a state and someone wanted to buy it but they wanted to keep it for sentimental reasons. However they had no interest in maintaining it or doing anything with it.
Why on earth you would leave a boat to get into this state because you want to "keep it" due to "sentimental reasons" is beyond me.
If I had no interest in maintaining my boat nor using it, I'd sell it - even if that meant I only got a couple of hundred quid for it. People are strange!
Not sure what sentiments they will be left with now...