After looking around for a while on the internet, I think that these films are the same as those used as 'privacy filters' for surf tablets, computer screens and mobile phones. See here (http://www.3m.com/3M/en_US/privacy-screen-protectors-us/?WT.mc_id=www.3mscreens.com). If so, then simply getting one of these from the local mobile phone shop or computer shop, cutting out a circle of the right diamter and attaching it to the speedo, tacho etc would solve the problem. I will get one and try it out and report back (if someone else doesn't beat me to it).
Cheers, Tim.
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