FUEL PUMP STOP SOLENOID
How do you know its breaking? well, for one thing, when you turn your engine off and remove the key....you may notice that it's still actually running..... So you need to stall it.
Mine turned out to be a poor connection, but I removed the stop solenoid anyway to have a look for any swarf in the hole (a sign that the pump is on its way out). Here it is seen from the camera on the rocker cover. The blue connector was my problem.
This isn't the correct way to do it, but you may notice that you struggle to get your 24mm spanner in the gap you have. So I gave a sharp blow with a chisel and that loosened it so I could undo it by hand.
Careful when you remove it, there is a plunger and a spring, don't lose the spring. If you look in the hole and see bits of swarf/grindings then it usually means the pump may need reconditioning.
Refitting is the reverse of removal, easy job, just awkward to get your fingers into it.