Discovery TD5 Slow to start... Help!

I am new to the forum, so Hi to all.
I have a 2001 Discovery TD5 with 195000 miles. I have replaced the injectors and about 3 days after I started having difficulty starting the engine. The engine just turns over and over as if it is starved of diesel. After turning over for 40-50 seconds it fires up with a cloud of smoke. I got the fuel pump checked and replaced it, I replaced the injector washers, I replace dthe fuel filter. I blew out the lines and pressure tested the pipework. All to no avail. The testbook does not show up any faults apart from the "3 amigos"(TC, HDC and ABS) and a SRS issue.
Can you suggest anything.....
Any help would be appreciated..

is this from hot/cold start or anytime?

Will start when warm, but when left to settle for a prolonged period, such as overnight, it will not start. It will just tuern over and over and over.... It will eventually start if you jump start, as the battery will run out of power, 40 50 seconds of turning over. Then it will run perfectly. Feels like the system is losing "prime", but I can't find where. |Could it be teh ECU?

After replacing injectors, glow plugs, wiring harnesses, pipework, fuel filter housing, fuel pressure regulator valve and some other bits and bobs, it transpires that the head was cracked. Sorted now.