I don't really eat chocolate that often, so m not madly angry, but I am very puzzled. Most manufacturers are going the other way and making their products veggie friendly, so why on earth are Mars going the other way? I do like the odd twix, and this will be annoying, but more than that I think it is a bad business decision.
As for rennet, it is in most hard cheeses, so I always buy cheese which clearly states it is suitable for vegetarians.
On a plus side...I've just stuffed my face with some vegetarian weight watchers chocolate bards which are even nicer than Mars Bars (though bloody expensive!). So i'll cope!
Vicky