Hi Paul

Two things, make sure there is no air getting into the fuel system from around the filter housing or pipes before the HP pump, and check to see if the filter on the end of the regulator is clear, but before you do that if you can get live data see if the pressure in the system on acceleration is getting near to the pressure the system is expecting,
the cycling of the locking maybe down to the multifunction controller in the under bonnet fuse box, there seems to be some sort of timer built into it, i have in the past come across a similar fault and i am still trying to get more info on this fuse box layout,

HTH Tom