Oldie,
I'm aware you were referring to political influence behind the disclosure.
However MI5/6 though supposedly the intelligence agencies for the nation, are by virture of the political system, nothing more than branches of the government, regardless of which party happens to be in power at any given time.
It is inevitable when you have someone as ambitious as Blair undoubtedly is, that '5' will be used as an instrument of the Labour Party and will do its bidding without question. If what I read elsewhere is true, they acted similarly against the NUM and CND on behalf of Mrs Thatcher (rightly in my view.)
As to whether its worthwhile - I'm sure that they got as much out of this 'terror cell' as they could. Clearly there is equal focus on moslems abroad from their sister service - yet not much if anything is, or will be disclosed about that aspect of this operation. Indeed it would be interesting to know how they got on to this group in the first place. It was reported that Menwith Hill picked up phone calls to people in the Mid East / Pakistan - though surely that can only be conjecture.
Should there be another attempt by a similar group, I am sure that successful interception will be equally widely trumpeted. When you allow the intelligence community or military to become politicised that is one inevitable consequence. Another, it could be argued would be the deployment of troops in a conflict with fudged objectives, unclear rules of engagement, and no apparent exit strategy.