Palestine Action are heroes. We should be singing songs about them, not prosecuting them.
Remember, legality and morality are only vaguely related. Beyond the natural crimes of murder, rape, etc. laws are just politics by another name. And the wealthy and powerful write laws to advance their own corrupt interests. Many moral obligations are criminalized, and many things that if there is a Hell will surely get you sent there are perfectly legal.
Those planes deserved to be vandalized. Hell, they deserved to be set on fire. It's a shame they weren't destroyed completely. If those planes are being used to carry out a genocide, then they should be destroyed. That is the simple absolute moral truth. If the law says otherwise, then the law is wrong. Anyone violating it still needs to keep the consequences in mind. But outside observers should not be afraid to speak truth to power. What Palestine Action did was not wrong; it was an act of heroism. The UK should be electing these people to parliament, not prosecuting them. Want courageous leaders who will actually stand up to powerful interests and do the right thing, even when it's hard? Well it seems you just found that exact rare kind of person right here.
Destroying planes that are bound to assist in bombing in Gaza is simply the morally right thing to do, regardless of the law. It's no different than a Jewish resistance fighter in the 1940s setting fire to a cattle train about to go collect prisoners for transport to Dachau. Sometimes destruction of government property is the only morally correct choice available to people.
And we shouldn't be afraid to say this. People in the UK should be contacting their politicians demanding a full pardon for these heroes.