Thanks for your reply. I did send an e mail and photograph to the garage; these are their two replies.
"Looking at the picture, it looks like the top cover is missing, i have spoken to the workshop manager regarding this.
At the end of each job the bays and worktops are striped down, so if there are any covers left off they are picked up quickly.
I also have checked in the store room where we keep a few covers etc from scrapped cars and there are no v/w covers in there.
I will ask the technician that worked on yours on Monday to see if he remembers anything too".
SECOND REPLY:
"Sorry for the delay in getting back to you.
We have contacted our local VW parts supplier and they do not list a cover for your registration. Therefore, we believe it came here without one.
We have also checked online and it appears only the diesel models have a cover fitted in this area".
Although I cannot be sure that it had a cover, I have had the van for five years and regularly top up the levels so when I raised the bonnet after the service (several days after when I returned to Wales having had it serviced in Wiltshire ) I was immediately "taken aback" at seeing things that I had never seen before! I have searched everywhere for photos which I have taken but I have none of the engine bay. This why I am convinced that a cover is missing!
I am reassured that this will not affect the engines performance but would be grateful if you could send me a picture and/or link to somewhere that I can purchase one or at least what it looks like for searching any breakers yards!