This insect was photographed on a nettle plant. I've looked at lots of photos on the Internet and I think it might be some sort of Ichneumon wasp but I couldn't get an exact match. In particular, I couldn't find anything that had the same pattern on the legs.
Yes, it's an ichneumonid - about as far as I would go I am afraid. They are notoriously difficult to id given that there are so many thousand UK species (how many 1000? I will check) and images would have to be very high quality.
Thank you for this - I'm new to identifying insects and at least I now know that I was on the right track. I'm finding that there are lots of very similar insects about and trying to pin down exactly what something is can be very difficult!