Engine Cuts out when slowing down

Hi have had my Vauxhall Astra Auto 1.6 for 4 years. over the last year when I slow down for roundabouts or traffic lights the power goes and the engine cuts out. It does re-start and the fuel gauge drops. I hate getting in my car now and I can't go very far in it. We traveled to Devon a couple of weeks ago and it cut out six times and then re-starts. It's so miserable it's becoming dangerous now and the car judders when going about 40mph then below that it cuts out, it could be anywhere and having children in the car its' frightening! It's been in the garage but no fault has been identified. Can anyone please help me and can tell me what the problem is and how to get it fixed I can afford a new car. I love driving but I really hate getting into this one.