Not forgetting of course that the loon who used to be in the RAF (flyover girl? Can't remember the name) claimed that her mum had met a friendly Arab who warned her not to get on the tube
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Carrot - no need to be paranoid, the police and security services are aware of dozens of plots at any given time. Only a few come to fruition and only a few get as far as a point where there is tangible evidence to bring a prosecution. I have no doubt that they were aware something was up, just nothing specific enough to do anything about it.