Radio Four comment from poeple actually working with Lennon at the time suggest he had nothing to do with the WRP but did submit some work to "Red Mole".
"Red Mole's" phones were tapped during this perios and Lennon was thought to have given money to a paper that survived entirely on donation.
As for the IRA Lennon watched Bloody Sunday unfold first hand like most UK mailanders at the time he was probably hhorrified by the incompeternce of what we Brits bill as the most professional army in the world.
Whilst "Red Mole" wasn't exactly for mainstream British values, I think it might be hard to "hang" a man for promoting freedom of speech.
As for contibutions to a proscribed terrorist organisation - that's a tough one. Nonetheless tonight in various pubs around NW London collections will be taken for that particular cause. It's not as if the practice wasn't and doesn't remain widespread.
It is a sad comment on our colonial history thatthe one part of our history that effects us worst today stands on our doorstep.