Well, just a late thank you to [MENTION=21724]cyccommute[/MENTION] and everyone else for the tips. I was happy to find a white spirit equivalent called Clean Spirit at the local paint shop (for only £3 for a big bottle), soaked the chain in it for a couple of days and find it came out really clean.
The weather is also suddenly so sunny here that I am about to finally lube the chain with Squirt and take my fair-weather road bike out on the road again.