Ah yes 'use' and 'development'
Having been down this road with my council, my understanding is this.
There is no 7 year planning rule. There may some legal weakness where a matter has been ongoing for a long period. There certainly is a policy in many councils to not pursue a matter that is more than a certain age.
There would appear to be a difference between "use" and "development" although my correspondence from the council confuses the two, even in a letter trying to draw a distinction.
Councils are slow to act where something is long established, they are also slow to act where a business is providing employment. If your 'neighbours' have been doing something for 20 years, the council would look foolish trying to say it was in breach of planning at this point.