They are not being charged because they protested, they’re being charged for breaking in and damaging a lot of military equipment. I think it’s a bit far to call them terrorists, but you can sort of see the government’s point, if you squint.
Out of curiosity, I looked up the US Federal definition of terrorism
definition
- the term "domestic terrorism" means activities that-
- involve acts dangerous to human life that are a violation of the criminal laws of the United States or of any State;
- appear to be intended-
- to intimidate or coerce a civilian population;
- to influence the policy of a government by intimidation or coercion; or
- to affect the conduct of a government by mass destruction, assassination, or kidnapping; and
- occur primarily within the territorial jurisdiction of the United States
Due to the element danger to human life, their definition wouldn't fit.
However, the UK legal definition
definition
- In this Act “terrorism” means the use or threat of action where—
- the action falls within subsection (2),
- the use or threat is designed to influence the government [or an international governmental organisation][^F1] or to intimidate the public or a section of the public, and
- the use or threat is made for the purpose of advancing a political, religious [, racial][^F2] or ideological cause.
- Action falls within this subsection if it—
- involves serious violence against a person,
- involves serious damage to property,
- endangers a person’s life, other than that of the person committing the action,
- creates a serious risk to the health or safety of the public or a section of the public, or
- is designed seriously to interfere with or seriously to disrupt an electronic system.
- The use or threat of action falling within subsection (2) which involves the use of firearms or explosives is terrorism whether or not subsection (1)(2) is satisfied.
- In this section—
- “action” includes action outside the United Kingdom,
- a reference to any person or to property is a reference to any person, or to property, wherever situated,
- a reference to the public includes a reference to the public of a country other than the United Kingdom, and
- “the government” means the government of the United Kingdom, of a Part of the United Kingdom or of a country other than the United Kingdom.
- In this Act a reference to action taken for the purposes of terrorism includes a reference to action taken for the benefit of a proscribed organisation.
is wild: no danger to human life required, merely serious damage to property suffices!
[^F1]: Words in s. 1(1)(2) inserted (13.4.2006) by Terrorism Act 2006 (c. 11), s. 34; S.I. 2006/1013, art. 2 [^F2]: Words in s. 1(1)(3) inserted (16.2.2009) by Counter-Terrorism Act 2008 (c. 28), ss. 75(1)(2)(a), 100(5) (with s. 101(2)); S.I. 2009/58, art. 2(a)