Please realize that other states are taking notes at this situation. They are waiting for US/UK/etc exec to visit and make the same excuse.
The US Congress can and has compelled appearance of non-US parties, and, while it may not have had occasion to resort to this for a non-US person (and hasn't used it's arrest power since 1935, relying instead on executive enforcement bodies and criminal statutes instead of it's recognized contempt and arrest powers), absolutely does have the legal power to send the Sergeants-at-Arms of each House to enforce such compulsory summons with force, to bring either materials or persons before the chamber.
Didn't the U.S. arrest a Volkswagen exec wanted in connection with the emissions scandal, when he visited?
The only potential exception is diplomatic immunity, and that is only granted to the few people who are directly employed to represent a foreign nation. (And even then, such immunity is voluntarily granted by the UK government.)
Other states aren't waiting for this at all; least of all the US. In the past when UK based executives of online gambling firms have travelled in transit via the US they have been arrested even before going through customs, in effect in international law it is somewhat akin to piracy, USG sanctioned piracy. This sort of creative use of laws to acquire information and/or people by various governments world wide has been happening for a very very long time.
No, arresting people who are not subject to any privilege against arrest in international law, who are on your territory, whether or not they have passed through customs, is not, in international law, in even the slightest way “akin to piracy.”
If I refuse to appear in court, I can be arrested and charged with contempt of court. Is that normalising a "violent response to a nonviolent action"?
Justice would be impotent in such a setup.