Thank you Gingejbee for saving me money. The manhole cover WAS the responsibility of the water company, you were right, and they came and replaced it this morning. They had to reduce the size of the opening and concrete it in, and put a new metric sized manhole cover on. I imagine it would've cost me quite a bit to get it done privately if I'd had to. I would never have thought it was the water company's responsibility, so thanks again. :-)
Yes, I'm here and delighted that it worked out just fine (and free!) ...and thanks for the feedback, it's really nice when people take the trouble to do that...thanks again!