All is not lost on the wine front, re-took the specific gravity of my elderflower wine & Hazel (at the Hill) came to my rescue showing me the error of my ways - It was my inability to read the hydrometer correctly that had caused the problem - it was not a faulty hydrometer after all......
The SG of the wine is 1.126 and it is fizzing away nicely!
Might just tell a white lie to the shopkeeper rather than expose my complete incompetence when I take back the replacement hydrometer that I bought this morning!
On a good note - I found some bungs on the internet that are for the plastic type of demi-john, so took a gamble and ordered 4 at 48p each & the postage was 1.90. I also got 4 one gallon bottles of water from ASDA at 95p each. The bungs arrived this morning & they fit perfectly, so this means that I have got 4 plastic demi-johns for 1.90 each. The cheapest I found them for on the interweb is 3.55 including p&p so I think this is a bargain!
I have also worked out that if I bought 10 bungs (7.30 inc p&p) plus 10 one gallon water bottles (9.50) then each demi-john would be 1.68 - even better still! because the p&p does not rise drastically for lots more bungs. The cheapest you could get 10 for on the internet is 2.57 each.