NON starter!!??

Ok, where do i start LOL A month or so ago i came back to the zed to find it started. I reversed out of the garage, went inside and found it had stopped. Not knowing how it stopped i pushed it back in the garge and went to work.

After work i removed fuel cap (lots of pressure) then the fuel pipe from the main inlet after the filter. Cranked for fuel to find fuel in the jug. I then went back to the filter (one that i changed last year) and emptied it out to see if there was any debris. Nothing. put back together. Cranked and then engine kicked in. spluttering due to fuel coming through.

Now, i have been driving for weeks. Been to two car meets over the weekend, one being in London. No problems. then boom. Same again. This time the car stopped when i was in it. Jumped out, opened fuel cap. No pressure. Removed fuel pipe ,cranked and nothing. Returned after work, cranked into a jug and half filled the jug. reconnected and nothing. Removed pipe tried again and quarter filled the jug. seemed weak.Tried two different relays. Same result. Just seems to loose pressure. Could it be the FPCU? im going to bypass tomorrow to see if the pressure maintains. Sorry for the long winded thread.