Thank you guys once again for the wonderful comments. I really appreciate the enthusiasm.
Yesterday I gave the beetle/schwimm a trial. Took it to deepest essex, drove cross country for a while, and have to report that the off road capability was fantastic. Then tried to reverse into the river (ready for a quick tow out if it all went wrong) The reeds and bottomless mud in the first location made it difficult to even get to the water. However, I eventually found a better spot in the river, but first went home and made a ridgid tow bar for my 4x4 Dodge truck. This enabled me to push the VW backwards into the water to see if it would float, and check for leaks. The rear end just started to float and no leaks, but the tow bar was too short to go further. This emboldened me to try and get it further into the water. My son was real keen to make the maiden voyage so I let him gently reverse into the water. As the front wheels were about half submerged, The water gushed in! - so Joe drove out quickly ........I took it home and found that I had forgotten to weld up some bolt holes in the front chassis cross member that were used to mount the old beetle body ...........
So, They were welded during the afternoon, ready for another try another day - I hope in the next few days