Letting those artists into the UK

The Observer reports that a number of artists are starting a campaign to fight the visa clampdown by UK authorities, which requires artists from beyond the EU to be fingerprinted, and organisations inviting them to pay £400 or £1000 to become 'an official sponsor'. (UK authorities are always good at charging their citizens....).  The Russian pianist Grigory Sokolov, living in Italy, recently fell victim to this policy, since he did not have time to travel to Rome to be finger-printed.

The UK Border Agency states that 'all migrants, not just artists, seeking to come to the UK to work or study, except for the most highly skilled, will require a certificate of sponsorship'.  

I wonder who decides who is the 'most highly skilled'. Do people have to audition, or in the case of scientists, send a piece of their most recent research? What are the qualifications of those who decide, and how long does it take them to decide?  Imagine if an artists suddenly falls sick, the Royal Opera House searches right round the world to find someone to take the role - do they have to ask if the singer has visa clearance, too?  Would, eg, Anna Netrebko, a Russian, pass this test? (She probably would, I seem to remember she was given Austrian citizenship for her achievements).