Brilliant, folks (gentlemen?). Thank you all very much as always.

Here's where it gets interesting. When (for instance) US passport-holders come to the UK as tourists, they can (usually) enter without a visa and are granted entry clearance upon crossing the border. As we know, this is usually for six months although is at the discretion of the agent.

However, in my friend's case, he has not only been given a visa but also already been given entry clearance, right? ISTR that the Tier 1 Post-Study work visa, after approval, gives him entry clearance for the full two years. Where does the discretion of the immigration agent factor into this? Could he be denied entry at any point in the initial two years of its validity?

In any event, I'm sure there will be no problem. He will bring the documentation with him which he supplied for the application, and will also bring the approval letter from his country's High Commission.

Fingers crossed!