What is wrong with my Vauxhall Astra Club (x reg)?

My car has an ongoing problem. The engine management comes on at the drop of a hat, and I have to change or clean my spark plugs really frequently as they keep getting fouled up, causing the engine to misfire. This has been happening for over a year, but has gotten progressively worse. I have recently been told there is an oil leak, but have also been told it may be an oil gasket.