Portuguese man-of-war found recently on the Cornish beaches. They can give you a nasty sting if you stand on the purple-blue tentacles. I think these are what we used to call blue bottles or blou blasie in South Africa. According to South African advice urine is good for pain relief if you do get stung, and always use salt water not fresh to wash the affected area. Conflicting advice in the use of vinegar. UK and Australians say yes, South Africans say no.
My daughter stood on a blue bottle when she was very small whilst with a friend on the beach whilst I returned home for something. Fortunately my friend rushed her into the pharmacy across the road where she was treated. I felt very guilty though when I saw her tear-streaked face and the red welts on her foot.