Nice one keeping it
yep, as far as I can see it's a Hill Special. I worked in a bike shop in the 70's and remember some of the details, the rear brake bridge is the killer ID for me as I can't remember any other builder that used the design, plus everything else matches, even down to the pencil stays and modified Legere lugs.
Headset might be a Brompton?
I can see some red paint on the front brake so likely a rattle can respray. Just need to remove some to look for some decals. Very fine wet and dry or acetone might give a clue used on the areas where decals would have been. Even in that condition its worth a few hundred quid...
I wonder if the chainset is original? Looks like a Williams which should have a date stamp.
Can you feel the twinge of jealousy from Cumbria lol