Zeef,
The UK Border Agency enforces immigration law in the UK. They do not make the law, Parliament does that. Google search working in the UK and you'll find the UKBA website. There are four categories of people who can easily work in the UK in any sort of job they can find: UK citizens, EU citizens, EEA citizens and anyone who has been granted limited or permanent leave to remain under Tiers 1 through 5 of the UK Visa system. There are no rules within Tier 1 to 5 making any special allowances for pilots.
The rules are very similar in almost every country in the world. If there was a shortage of pilots eligible to work in the UK under the above categories, they would change the law to create a special category for foreign pilots, just as there is a special Tier for foreign doctors and nurses in the UK due to the shortage of UK medical professionals.