Defender td5 intermittent starting

Hi all,new to the forum but not land rovers,would like any sane advice regarding problems with starting. Its a 52 plate defender 110,always started on the button & ran really well but....about a month ago starting got steadily worse until it finally crapped out after a short run & refused to re start. To date have changed-
Injector seals & copper washers (genuine L/R)
Injector harness
Fuel filter
Cleaned wiring loom to ECU plugs(small amount of oil)
Had a diagnostic on the ECU & was told its OK
Fuel pressure regulator was changed approx 3 yrs ago
Was told the fuel pump was suspect so have changed that as well after which it ran fine for a couple of days but now we're back to square one.
Any help much appreciated.

Is it turning over normally, is battery fully charged, can you hear fuel pump running, check fuel pump and starter relays and connections, is fuel reaching the FPR.
Could be faulty or loose crank sensor, or poor engine earthing, Just stabbing in the dark really.

We put a new battery on 2 months ago,been fully charged & turns over nicely. fuel pump a little noisy for a second then quietens down(brand new one fitted at weekend)
Car ran well for a day after new pump fitted but then conked out & refuses to start,a little white smoke from exhaust on cranking if I press the accelerator but no attempt to start.
Will have a look at relays & connections etc as you suggest.,Thanks for the ideas.