The Petrol Cap on My Ford Ka has fell apart. How can I fix it?

I collected my year old Ford Ka1.3 Design 3 dr 2005 yesterday & when I took it to fill it with Fuel the cap came off OK but then fell apart. I now have a spring that obviously fits inside somehow but I cant get it back together again and am unable to get my petrol cap back on.
Any ideas?
alison, December 2006
hi
yeah the retaining washer has come off which holds it all together.... they dont cost alot and are easy to fit ...... take the car back and play hell with them .

anon, December 2006
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