Back in 2004 many, many passengers in the US were chatting about suspected dry runs being carried out on a number of airlines. It was suspected that cells were carrying individual components onto planes and timing drills of assembly in the flight restrooms. http://www.womenswallstreet.com/series/series.aspx?cid=9
My flight from Orlando to Chicago had me on edge. There were 5-6 arab looking men with paper lunchbags in the waiting area sitting together. When they boarded the plane they had seats all over the aircraft. Each on got up and used the 'restroom' midflight. I remember trying to figure out what could be used as weapons and resolving in my mind what I would do in the event of a hijack.
Needless to say nothing happened, but it does make one go hmmm....
Per BBC Radio, house surrounded and being searched in High Wycombe, a London suburb.
Most short flights cancelled until 2pm GMT, but some longer flights still departing.
Might just be the ingredients for their old standby, "The Mother of Satan".
They'd use the tissues to filter the precipitate, probably in the toilet, and as soon as it dried, impact alone could detonate the stuff. Plenty of time on an overseas flight.