S3 starting problem

[s4mark]

Hi. My S3 has developed an intermittent problem recently and is starting to get worse.
It has always started first time immediately on the turn of the key but has recently begun to take a while.
Sometimes when trying to start it will turn over for about 5 seconds before spluttering into life. Once started it runs fine, idles a little lumpy but has since I've owned it and it's only slight. It will then start fine for the next few times before doing it again. I have noticed a smell of petrol under the bonnet when I was changing the air filter on Saturday but couldn't see anything obvious. Could it be flooding itself a bit occasionally?
Any advice would be good if anyone knows what i should be looking at specifically or am I looking at an expensive trip to the dealers?

Thanks

 

[Maz]

Check the voltage on the battery, it may be on its way out.

 

[s4mark]

thanks mate had the voltage checked but all seems fine.
when i try and start it first time it just turns over and over, if i stop and try again it starts first time
do you think it may be worth changing the plugs now?