I've seen a lot of non-competes in the UK around mid-management and sales positions. But I don't recall any business I know ever successfully enforcing one. Generally speaking, if it gets to tribunal and the ex-employee can reasonably show that they left the business as a result of constructive dismissal, the tribunal has taken the view that the non-compete is voided by the circumstances of termination.

The only time I've heard (very much third-hand) of one standing wasn't the non-compete being enforced, it was the fact of the ex-salesman being caught emailing himself the entire customer and contact list, which is slightly different.