From your Guardian link:
"We lost control over our borders almost two decades ago. In 1998, Tony Blair removed exit checks. Nobody checks your passport once you have gone through security at an airport, as they do in virtually every other country in the world"
Arrant nonsense off the guardian.
http://www.mirror.co.uk/news/uk-news/uk-passport-exit-checks-everything-5476792
The link is several years old. Things have tightened up further since then.