BMW Repair: red oil light come on, oil pressure gauge, oil pressure switch

Question
I have had the red oil light come on in my BMW year 2003, model 318i, I have had it checked by the RAC who have advised not to use the car at all as the engine will get jammed. He has said that there is a problem with the oil pump which is probably blocked or needs replacing. What would the approximate cost be for the replacement of the pump if it is done at the BMW garage? Can it be replaced by somebody who has some DIY knowledge or is it too big a job? Is it best to have it done by the Main Dealer?

Answer
If there is a light on(the red one)it is saying that there is low oil pressure.Now the first thing I would do is check the oil pressure with an oil pressure gauge,to see what it really is.When you remove the oil pressure switch it should be dry on the outside of the switch,if it is wet the switch and soaked in oil then it needs to be replaced.Many times that is all that is wrong is the oil pressure switch.I am not familiar with any blockages.And if they oil pressure is low just replacing the pump won't fix your problem.Pressure is made by the clearances in between the crank and the bearings.So they would need to be checked if it is low.An engine overhaul would be the time then.I am not sure who RAC is but I think they have jumped the gun alittle with out actually checking the oil pressure first.