Guddering sound/ struggling to start after a journey

Hello, I have a Volkswagen golf mk4 1.6 petrol

Just had the cat done a week ago. The last few days my car has been making a juddering sound when its started "ticking over" i travelled 20mile in it. And I jumped back into my car and it wouldn't start. Took about 10 attempts to get it running. The next day I parked at tesco went in come back it failed to start had to leave it over night come back in the morning and it started fine. Can any body help. Hope I've explained right..

Waz