they cannot misuse their legal powers, as parliament is Sovereign in the UK.
Facebook took the risk by not complying with the wishes of a sovreign state, and that state then takes legal action against facebook.
facebook arrogance in this matter is staggering, and by some could even be seen as a direct confrontation with parlaiment.
If parliament did not respond, it would look weak and in some sense even delegitemize its sovereignity. If they backed down on facebook's apperent arrogance, what is stopping other companies from trying the same.
Let's not forget mark zukerberg was summoned before the parliament. Ofcourse he could decline (mainly because he is not a UK citizen), but being summoned is quite a big deal considering they (uk parliament) is literally asking you to come over and explain what your doing..
don't be suprised there are rammifications when a state asks for your presence, and you arrogantly decline it.