Can you run different width (225 & 235) tyres on an A3 Quattro?

I'm running 19" 8.5J Alloys with 225/35 tyres all round on my A3 2.0T Quattro so there's a bit of stretch. However, I got a bad puncture the other day and need to replace two of the tyres. I wanted to take the opportunity of fitting a pair of 235/35s as I'm positive they'll fit (and will offer the rims more protection) but the garage has advised all four tyres need to be same size.

I don't want to replace all of the tyres as two of them have loads of tread left. I can understand you not having different size profile tyres as I guess you could potentially have the front and rears rotating at slightly different speeds but I'm unclear how having a 10mm wider set of rear tyres would adversley affect the car.

Any guidance would be greatly appreciated!

Thankss

OK, thanks I appreciate your reply. So given the Haldex system is not like a full 4x4, would you say this is an acceptable difference or is it likely to cause problems? Ultimately I would like to change all tyres to 235/35/19s but at the moment two of the tyres have a good 5mm on so, so my preference would be to not just throw them away.

Excellent, cheers for your help. A pair of 235/35s it is then!