In the UK employment law prevents an NCA restricting a person's employability.

My NCA and employment contract says that I cannot work for a competitor in the specific line of business within a 40 mile radius.

If a company wanted an NDA restricting a person's employability then in effect that person would remain on the company payroll on "gardening leave" or "on sabbatical".

When I worked for a local council I had to sign the official secrets act. Even at the height of the cold war I can't imagine that poll-tax rates and refuse collection days were of much interest to the KGB. Excessive regulation leads to contempt for the regulation.

There is the spirit of the law and the letter of the law. We all understand and respect the spirit. The letter of the law is to ensure that the spirit is quantified and implemented fairly. Where the letter of the law fails to implement the spirit of the law is undermines the principle of law.