Snickers workwear is amazing - lasts for years. My brother recommended it to me and he's a carpet fitter so needs the toughest. I've had two pairs of thier trousers - no wear after 3+ years of crawling under desks. Not cheap though - but then nothing good ever is...
http://www.snickersdirect.co.uk/snickers-accessories-c-5148.html
This man speaks sense! We have Snickers work trousers here, in black. I also wear them to do the garden, go fishing in, and they still look good!
We WERE required to wear smart shirt, trousers and a tie, but we soon knocked than on the head! Even a four quid shirt from Asda is a waste when it's covered in toner Now we wear a black polo with the school logo on, Snickers work trousers, black trainers. No ID badges whatsoever though. No staff do here.