Have never seen anything like it def not a standard fitting issued by any company by state of that union it looks like its not been fitted today and was existing.
It was fitted by Eon almost a year ago as part of fixed price tariff they had to have smart meter. I’ve been to do boiler service and on doing drop test it dropped 5mb so started hunting down through the usual suspects and ended up here. When I sprayed the joint with LDF it sealed it up so held for drop test. Wouldn’t bubble or set sniffer off. I connected hand bellows to give a bit more pressure and that’s when I got some bubbles.