I was pretty sure they were snake eggs, because I've seen grass snakes on a number of occasions in our garden, and a few months earlier, my dog had disturbed a large grass snake sunning herself under a piece of old carpet, not far from the manure pile.
A call to the RSPCA proved fruitless (recorded message, abrupt disconnection). My second call, to a friendly lady at the Amphibian and Reptile Conservation Trust (www.arc-trust.org) was more helpful. Following her advice, I carefully removed the eggs to the Wild Garden. I laid them near the pond, on a bed of manure, and covered them with more manure, so that they would stay warm. The eggs should hatch in late September - early October. I'll update you when I know more!