First of all, Google's TOS says
we reasonably believe that your conduct causes harm or liability to a user, third party, or Google — for example, by hacking, phishing,
harassing, spamming, misleading others, or scraping content that
doesn’t belong to you
And you ask:
But suppose a researcher, say based in UK, managed to work around
them, get a big amount of data from Google searches and use it to
publish some research.
You're confusing methods with results. Someone uses methods to get a result, but if the results are not legal, the methods are usually illegal, too.
Would the above depend on how they circumvented Google's checks (i.e.,
by using lots of proxies)?
The words "or scraping content that doesn’t belong to you" means just that; it does not give any wiggle room for the actual method used to scrape.
Could they get, theoretically, into trouble?
Very much so. The researcher would have at least civil liability, and possibly criminal exposure.
Would they, practically?
Google can be very not kind to people who break their TOS. And Google has lots of money to spend on lawyers and court fees to enforce their TOS. Google would probably be able to easily prove the data came from their servers, and would probably have server logs to help prove it.
And see user6726's answer for specific legal citations in the US and UK.