Did you read the article ?
It says "The Office for National Statistics (ONS) has changed its methods for calculating immigration by using people's interaction with public authorities as opposed to surveys."
So they changed the method, and the numbers jumped.
That's because when you leave the country, there is no form to fill in.
So it can only be estimates. And they have changed from airport surveys to checking if NI numbers are being used.
When I left the UK, I just stopped direct debits etc, and went.
No paperwork to leave the UK, the paperwork is on the other side, work visa and all that. That is the difficult bit.
What really interests me with these stories though, is where are all these people going? What magic country is it that UK folk can just go to, no stringent visa requirements, and milk and honey flowing down every mountainside ?