I had exactly the same problem with my polo, same model and engine, and found it was damp in the ignition circuit and a bad coil earth.
I used some spark testers first to see if i was getting a spark (these look like plastic spark plugs, that go inbetween the ht lead and spark plug, you can pick them up from halfreuds etc for a couple o quid) took apart all ignition connections, wiped them clean and dry, and bolted down the earth lead from the coil.
Worked for me.