This will be the fuel evaporative emission valve.Nothing to be concerned about.They all make this noise,some more noticeable than others.

Haven't heard about that. How does that work, and where is valve situated? I do know the car uses too much petrol in comparison with previous Corsa I had, even allowing for extra weight. Oil gets dirty in no time at all.

there is aknown issue with the camshaft caps comming loose making them sound tappety, causing camshaft whip & eventually snapping the cams ! & then dire engine damage !

Always best to make sure yours isnt one of these

below is an extract from a consumer action group

http://www.consumeractiongroup.co.uk/forum/showthread.php?275141-Out-of-warranty-claim-for-Vauxhall-Corsa-camshaft/page3

When this problem occured to my daughters car, (4 young women broke down on the M6 300 miles from home) I had never heard that there was a problem with these engines, I thought it was just bad luck, It was a struggle to get them home and then gave her a real problem with transport, luckily we had another Corsa she could use. The AA man diagnosed the problem and he was spot on, I took the car to a mechanic I use and that was when we found the broken cam cap as well as the broken shaft, at that time I thought the shaft had snapped and taken the cap with it so I contacted Vx customer care and asked them whether it was unusual that a camshaft should go after 60K. It was then that I discovered that there was a problem with loose cam cap holding down bolts and Vx had known about it and failed to issue any sort of warning/instruction. I don't know what fact you want, Vx have confirmed there is a problem, the holding down bolts come loose allowing excess movement of the camshaft and causing failure, as an engineer are you saying that this is not what is happening? I doubt that you would say that its OK and that loose caps are something that the shaft can cope with so as an expert what sort of failure would you expect from loose caps?