You are a knowledgeable lot! Once you all put me on the right track I've pinned it down to Sun Spurge - Euphorbia helioscopia.
As you pointed out Exdancer the sap can cause blisters. However on one website I searched it said about the sap: "In Plants Britannica, Richard Mabey mentions that Manx fisherman applied the sap as an aphrodisiac, and that its name in Wiltshire was ‘Saturday Night’s Pepper’ ". My mind is boggled thinking about it
. Thank you for all your help x