Peter, I have to ask you this question to ensure I haven't overlooked something that could change the whole complexion of the problem. You didn't, by any chance, add a lot of extra oil to the sump just before all this happened did you? Overfilling with oil could result in oil flooding through the breather system. The classic cause of overfilling is to fill a dipstick engine with oil as if it were a level plug engine.
If the oil level is where it should be, and you have hardly any compression, it sounds more like a cracked or slightly perforated piston crown than anything else, though badly broken rings could do it. Unfortunately that puts us back into the prospect of overhauling the engine: dismantling, removing piston, cleaning and inspecting piston and rings plus cylinder, replacing defective parts, and reassembling. This isn't terribly difficult stuff, but it does require some basic tools and getting yourself quite dirty with black oily stuff.
Please clear up the oil level question, and let's see if anyone else has a better diagnosis than mine. If not, I think you are going to need some spanners.
