Been back along to the garage tonight so they could run diagnostics again. They said they usually just repair the AKF pipework on 1.0l models, as per the main dealer guidance they receive, and that resolves the fault. The main dealer guidance for the 1.5l model is to replace both parts together so they reckon this will solve the issue with mine but said its unusual on 1.0l models, apparently. They are still charging for labour but after checking the cost it will be £140 in total for the charcoal canister replacement and they said they will take it on a longer test drive afterwards and run diagnostics again to check its resolved the issue. I have booked it in for next Friday so will update as to whether this has resolved the issue. Out of interest I got a quote from the main dealer and the cost to replace both parts is £428.16, not including diagnostics. So far the VAG specialist is £350 including diagnostics.