and especially for anyone visiting the UK as a tourist on a visa waiver.
Just to add the comment that there is no visa waiver programme in the UK. Visa Waiver is a USA concept, and we have nothing comparable to it. Everyone in the UK who does not have ROA or citizenship in the Common Travel Area (CTA) needs to have a visa. Including US citizens.
Having said that, a business visitor may attend meetings, seminars, take courses, engage in consulting, and attend job interviews. IND does not distinguish between the regulated activities of a visitor or business visitor. And it is certainly within the rules for a tourist to attend a job interview.
The catch is that they need to be invited for an interview beforehand, when they are outside of the UK, and it needs to be declared at the port of entry or you can be in *trouble*. With the new rules coming into force, this should not be much of a problem because the company will get done if they are breaking the rules - so they will be more sensitive to it. So if they are interviewing a foreign national, they will need to show that the vacancy has been listed publically for 14 days, and UKvisas is far from naive.
Now having said all of that, returning to the advocacy side... There are some outsourcing firms who will take a promising candidate and arrange 'n' number of interviews with their clients. And it's a way to get a shot at 5 - 10 big companies in one go. On the downside, it needs to be a true outsourcing firm and not an employment agency. They need to have an outsourcing relationship with the client for it to work rather than a simple PSA for candidates. If that's in place, then it's a green light. This has already been upheld in tribunal.