"treason, violation by a subject of his allegiance to Sovereign or State ..."The actual definition goes on to add "punishable by death" which, you'd have to say, is one of the things wrong with it, assuming you are opposed to the death penalty. Then again, just because it's punishable by death does not mean that death is always imposed, or ever imposed.
But why the sudden interest? Well here is a quote from a man who had some association (but not in any criminal or conspiratorial sense) with the July 7th suicide bombers:
"It started with the anti-war movement in 2003 – they were expressing their willingness to kill British soldiers abroad. I thought these guys were going to join the Taliban."(this is quoted from the Telegraph: link)
Whilst not being a lawyer, it would seem to me that a statement of this sort, if actually representing peoples thoughts, is easily treason. So what, you may be thinking. Well the point is that if these people had been convicted with treason it seems very unlikely that they would have gone on to carry out their bombings. Mostly because they'd be in prison, one hopes, but even if that wasn't the case, the kind of terrorism we face thrives in secrecy (as does all terrorism really). Even a charge of treason would expose the general environment in which these people were living and that in itself would reduce the risk, just by drawing attention to things.
This is not to say that use of treason as an offence will eliminate the threat we face, but at the moment even getting people to the point of being charged is proving difficult and mere interdiction of plots (I say mere, whilst recognising the effort that that involves) will only hold the line. A charge of treason would allow an early intervention but more importantly provides an opportunity to directly address potential terrorists before they become actual terrorists.
By contrast current policy seems entirely aimed at legislating to reduce civil liberties whilst justifying this by reference to "secret briefings" (of the threat see: link), with the classic side-effect that the consequences of such policy fall equally on all of us instead of being focused on the offender. Why introduce new legislation, why not use existing statute?
By the way, the notion that the law abiding have nothing to fear from such legislation is completely bogus. I don't need to be actually arrested for the liberties under which I live to be reduced; generally speaking that attitude is the first step towards a police state.
Treason, that is a charge of treason, is not something we should be ashamed of. We are all citizens, it is entirely reasonable that we should expect the same degree of loyalty from all our fellows. When this is lacking we should have the confidence to say so, and where necessary take action. After all we now know what failing to take action can lead to.