Thanks for that had a look at left side drain (which is side water coming in) and yes it's blocked - I think that combined with the centre drain being block was more than enough to cause issue - I had cleared centre and checked by pouring water in - had a probe into left side drain and cleared again water tested - will lift trim if it ever stops raining and clear out - doubt if it's ever been done. have left bucket inside just in case and over mat is in boiler room drying out -
TonyB aka Rob Skytoon