I too was thinking that this sounds like the old injector seal problem. There's tons of info about it on here.

I was however under the impression that the injector problem was likely to result in turbo failure due to the oil feed gunging up long before the rest of the engine sludged up?

The oil pressure switch on most engines monitors the pressure just after the pump outlet. So, if there is a loss of pressure it is more likely that:
# the pump is mechanically worn and not able to raise the pressure sufficiently
or
# there is sludging in the sump and especially around the pick up gauze which is preventing oil pick up
# oil level is too low and the pump is picking up airated oil

Oil level low: easy to check and rectify
Sludging in the sump: requires inspection. Easy enough, just drain the sump and look in through the plug hole with an inspection camera
Worn pump: needs inspection and replacement - no idea how easy this is on this model

Sludging elsewhere in the engine would cause oil starvation to some areas, but surely would not result in low pressure, but more likely high pressure causing the relief valve to open??? comments anyone???

I don't think there is enough information to offer a truly considered diagnosis, but I'm inclined to suspect this vehicle does lots of short journeys and isn't really having enough oil changes to suit those conditions (and maybe the changes are being done by sucking oil out the dipstick hole??). Sludging is the end result causing lack of pick up and low pressure.

The oil pressure light "blinking" occasionally whilst driving suggests that the pump is having a hard time keeping up the pressure and that you are driving with low pressure all the time (low, but not necessarily critical)

Hi , thanks for your post. It is a 2 litre tdci. We were told that the turbo was clogged up so we used the same as the Trade industry use, sorry I may have described this incorrectly.

Thanks

I believe that a lot of these turbo problems are due to the extended oil change intervals designed to appeal to fleet buyers, I'm sure that if the oil was changed twice as often a lot of these failures wouldn't occur.