The Daimler Dart was probably the first British 4 wheeler, but I don't know about three wheelers. Wiki on Reliant fails to give a date for full body manufacture:
http://en.wikipedia.org/wiki/Reliant
However, Glasspar seems to have been the first production (though not necessarily mass production) glassfibre car:
http://en.wikipedia.org/wiki/Glasspar_G2
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-----------Wasn't it 1956 and the Reliant Regal Mk3?
---------------------------No, no charm at all. It's a shed.
-------------------------------The Allard Clipper. 1 x door, 1 x bench seat. 1 x wheel drive. Dickie seat behind cabin to safely isolate 2 loud and sticky children.
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----------------------------There are many claims and counter claims about who made the first series production fibreglass cars (yes, it's a loose term here), but the Allard dates from 1954, so that's one marker down.
----------------------------------------------Yes exactly, it's why I dislike the things too![]()