Since even British officials are now backing off from the theory that the London bombs were the work of men who intended to be suicide bombers, we are left with trying to determine what the four of them thought they were doing.
The authorities would like us to believe (or here) that their Islamic terrorist handler misled them into believing that the timers in the bags was set so that they could get away before the bombs went off. That still doesn't explain why they seemed so cavalier about being seen together in video cameras.
Some conspiracy theorists believe that the four were tricked by an intelligence agency handler into believing that they were participating in some sort of terrorism preparedness drill in the London Underground. While it is possible that they were tricked that way, it seems to me that it would be very implausible to them that they would be picked out of Leeds to perform a job which could easily be done by some intelligence operatives working out of London.
I think the most likely scenario is that they were tricked into thinking they were involved as drug mules in the movement of drugs from Leeds to London (see also here). They would have no need to be concerned about the video cameras, as they would have no fear of being seen together and leading authorities back to their 'cell' (which of course doesn't exist). The rucksacks too big for the bombs inside might have been filled with stuffing intended to feel that they were filled with drugs. Their instructions would have been to meet with someone either on a particular subway car or bus, or at the end of a particular subway or bus route, and hand over the rucksack. Then they would all assemble at a central location in London to receive their payments.
No Islamic will or video celebrating suicide, no public celebration of the 'martyrs', unsatisfactory assumption of responsibility, overly large rucksacks, happy-go-lucky bombers with no concerns about being videotaped together or leaving behind identification that would lead back to the 'cell' which supposedly had plans for future attacks, uncharacteristic candidates for suicide bombers - it all adds up to one thing. Someone tricked the four into believing they were drug mules. Once we accept that fact, we have to accept that there is absolutely no reason to believe the Official Story that this violence was connected to Islamic terrorism. It could have been set up by anybody, including the intelligence organization of any country. Of course, the fact that four Muslim men were chosen as the patsies gives us a clue as to who might have been involved.
Unfortunately, British authorities seem to be in on the cover-up. The peculiar transformation of the original certainty that the bombs used were military plastic explosives - and this would be a certainty as their analysis would be based on chemical residues - to the theory that they were a home-made mix in the Egyptian patsy's bathtub, indicates that the British investigation has become completely corrupted. Military explosives were in the rucksacks, but since the investigators couldn't tie military explosives to the four bombers they had to attempt to frame the Egyptian by claiming he made the explosives in his bathtub. Now that the frame-up of the Egyptian has fallen apart, the whole cover-up has also fallen apart. Who are the British authorities trying to protect?