There's no external oil leak and the dipstick level is fine. The oil light first came on a week ago: I was at traffic lights and realised I needed to be in the other lane so accelerated hard to make sure I'd be ahead, light flickered on at about 4000rpm in first gear.
The next day it came on whilst I was on a dual carriageway, so I stopped and called out Green Flag. They couldn't do anything with it and I drove it two miles home with no issues. Next day went to work (three miles or so) and no issues but the light came on just as I was getting home. I'd been very careful to drive gently.
Took it to ATS and they replaced the pressure sensor switch to no avail. They found evidence that the sump, DPF and turbo have all been taken off in the past but couldn't say any more. It's now at an another garage and they haven't found a solution yet.
I've had the car since January, it's only got 67,000 on the clock and it's got a clean MOT and nothing wrong on the major service I just had done. Any ideas what could be going on?