I commented on the Instagram post and Mitchum asked me to contact them which I did. They have now emailed me, asking for photos of bottles showing batch numbers, photos of injuries incurred, and asking for proof of any doctors visits or medical costs incurred.
They are offering £7 if taken in vouchers or £3.50 if taken in cash. I don't physically go to supermarkets that often, but I suppose I could get a friend to use the vouchers in store for me. I have several bottles, but it doesn't seem much compensation for the pain caused, as I was itching and sore for days.