HELP - Low oil pressure, swarf in filter, loud ticking noise

[mobilejo]

After finding out that my misfire on 2002 X5 4.6is was down to a leaking head gasket, and getting that fixed and having the car run perfect for 500 miles or so, a new (or seemingly new) problem has occured;

Today when driving I started hearing a clicking sound coming from the car and started to look for a place to pull over, as I made my way off the dual carriageway the low pressure warning came on. I stopped and the oil was low, towards the bottom of the dip stick. I topped it up - took 2 litres to get to the top of the dip stick - and started it and the sound went away. Drove off and within seconds the sound and the oil pressure warning returned.

Had it towed to my mechanic who checked the oil filter and it has alot of swarf in it. He flushed the oil system and changed the oil and put in new filter (as the filter was clearly blocking the flow of oil due to the swarf). It sounded fine once running again but as soon as I drove up the road the sound came back and the oil pressure warning came back.

It appears that whenever its topped up, all sounds normal and oil pressure seems fine but as soon as the car is driven just a few meters, the pressure cannot be maintained and the oil does not circulate. The noise seems to occur when the pressure drops and oil is not reaching all parts of the engine.

The mechanic is going to strip down the car - sump, oil pump, timing case, rocker covers etc - everything off for full inspection. However I am interested to hear what you guys think may be the problem. And where the swarf has come from...