Was cleaning out some weed from the pond 2 days ago(I'm in UK) and looked
down to see a small black slug type thing on my ankle. I pulled it off, but
it had been attached to me and left a pinprick of a hole. Over the last day
this has now swelled up and redness has spread. I can hardly bear weight on
it.

Was it a leech? If not any suggestions, and do I need medical attention. Are
they poisonous, whatever they are??

Tony