I'm saying it is outrageous for the UK government to use a UK law that was put in place to deal with extreme circumstances involving terrorism and threats to national security as a thinly veiled threat in a case that revolves around someone wanted for questioning about a rape and sexual assault, yes.
Especially when making use of said law might very well be in violation of international treaties, and have severe implications for the diplomatic protections of embassies worldwide.
You're mixing up "mention" and "use", which makes it very hard to understand which you mean. Maybe what you're trying to say is that it would be outrageous if they invoked that statue.
No. I meant what I wrote. It is outrageous that they are using the law in question as a threat.
I'm sure I could have formulated it otherwise, but your suggestion states something different, which implies no condemnation of the action they have already taken: They have already used the law in question as a threat by mentioning it in their letter to the government of Ecuador.
Actually making use of it would not merely be outrageous, it would be a violation of international law.
Especially when making use of said law might very well be in violation of international treaties, and have severe implications for the diplomatic protections of embassies worldwide.