So was trouble shooting a few ideas from OZMPS and I went to make sure the car would idle (to rule out the in-tank pump being faulty) and the pump sounds like marble in a tin can
Pulled it out and refitted stock internals on stage1 and now it holds pressure fine, but the cause seemed to be the circlips.
One of them was in the spring the other was bearly in place. This has caused serious damage to the internals but luckily no damage to the pump itself.
Photo to reference the spring and the top where the circlips should be.