The "Le Mans" filler cap is the flip up alloy fuel filler cap. Standard on all the Classic four wheelers and those have a lockable cap under the flip up cap so I assume the 3 wheeler cap is also similarly lockable.
Is it alu finished (i.e. matte) or is it one of those chromed ones?
http://holden.co.uk/displayproducts.asp?...uel+Filler+Caps (second & third row)