Citroen Xsara oil leak

I have high pressure building up in my engine which is causing oil to spit and bubble out of the filler cap. Also after a short drive when we took the dipstick out oil sprayed out everywhere. Oil is leaking out really badly, which we think is coming from the oil filler cap, but we are not 100% sure.I have white smoke coming out of the exhaust sometimes when I start the car up and when I pull away from junctions, but not when I am driving along.I have had this problem for 4 weeks now. I took the car to a garage and they said that the engine is on its way out, but this doesn't make sense because apart from a little judder I get when I first drive the car due to needing a new ignition coil. The coil problem I had before the high pressure build up and oil leak. My car drives lovely, its doesn't overheat,it doesn't have any knocking or tapping, there is no oil getting into the cooling system and the car starts first time with no trouble at all.Can you please help.