starting the car up I noticed after around 15 minutes of the engine being on the car started to idle roughly and there was a stronger smell of petrol before the car completely cut out. I started it again but it would just keep cutting out unless i held the revs up. 

The whole journey home the car would cut out when I was slowing down for lights or roundabouts as the revs dropped. 

The battery has been ran flat recently if that could be linked with this? Any ideas? 

Hi

 

Not sure if relevant to your Impreza but had the exact same symptoms on my Legacy R, It was a faulty EGR valve. 

Regards

Steve