In the UK, no such agreement exists. Source: I know people who would have been required to sign it. They confirm that they would have it screened both out of

In the UK, no such agreement exists. Source: I know people who would have been required to sign it. They confirm that they would have it screened both out of a sense of duty, and a desire to avoid accidental breach of the Official Secrets Act if they ever produced such memoirs (release it to your agent with something you thought had been declassified? 30 years in prison for you!), but they were not explicitly asked to sign such an agreement.