declared for all the world to hear...
I've just brought a car which has a built in phone and uses my phone sim.
Therefore I need a duplicate sim for the car.

Vodafone and Orange seem to have a multi sim option. However, I'm on O2 and
they offfer nothing like this.

Has anyone tried (and yes, I know they are illiegal) a duplicate sim maker
like http://tinyurl.com/naoh5 this successfully for this purpose?

They aren't illegal, they just don't work, except on very very old SIMs.
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Regards
Jon