The original manufacturer (Newton Equipment) put me on to a company called Think Automotive (think auto.com).
I dealt with a guy called Santino Meale who sent me a new one for about £20 delivered. I seem to remember that it looked like they had changed the moulding slightly to make the problem less likely.

Fitted the Newton company`s billet saddle to the fuel cap after struggling with a jammed cap from the usual swelling plastic part of the cap. Part number SAD4M . If the cap has a lock then you have to ease the rear part with a file to allow it to clear the milled groove . I also noted that on an original British supplied cap the centre thread for the nut is not long enough to allow the Nyloc to bite when converting to the ali saddle so I turned it upside down . The other one I fitted to a Taiwanese supplied cap had a longer thread. These worked out at £24 each for five posted from Newton Equipment . If you only want one It works out a fair bit more.

:headbang: fekin plastic shite
usual story the feker has expanded , jammed in the filler neck...
dismantled /sorted/ sworn at in great depth

yes i know you can buy an aliminium replacement but seems a lot of money to me

William fire up the angle grinder

rant over