I have just had a good look at it and it is only the top 4 cups that are damaged, but I must say down where the ball gets hit by the hammer has worn through the plastic and is just starting to damage the back picture so it may be a case of replacing the plastic after all. 
Is it this I need? I only see 1mm or 2mm. It's free postage if you buy 2 sheets so it's not that bad.
http://www.artstore.co.uk/clear-styrolu ... 297-p-7700
Sorry, I found the one you mentioned.
I managed to find the same stuff on eBay so I ordered some. Any good tips on what to use for the holes?

Is it this I need? I only see 1mm or 2mm. It's free postage if you buy 2 sheets so it's not that bad.

http://www.artstore.co.uk/clear-styrolu ... 297-p-7700
Sorry, I found the one you mentioned.
I managed to find the same stuff on eBay so I ordered some. Any good tips on what to use for the holes?