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Dr Alford, being a professional, may not have chosen to mix up something as volatile and dangerous as TATP - or if he did he may have taken steps to desensitise it somewhat, not wishing to foolishly blow himself up.
(Your correspondent once spoke to a forensic-explosives boffin from the UK gov lab at Fort Halstead, who described his reaction on being nonchalantly handed several pounds of a similar compound by a blissfully unaware copper back in the pre-9/11 era. He said it had taken years off his life.)
Dr Alford's mix apparently required a proper detonator, whereas proper mad-bomber TATP can be made to detonate using no more than heat or electric current.
Really good terrorists, as Dr Alford points out, can build home-made detonators which could conceivably be smuggled through security buried inside an electronic device. The Provisional IRA could do this, and not being suicidal types they had reason to; but proper barmy suicide fanatics would be unlikely to bother. The whole point of having dets is that most of your charge can be comparatively safe to handle and move about, and the det - which will go off if shown any disrespect - can be kept separate until the last moment and babied.
As of 2005 there were indeed several murderous jihadi scumbags resident in the UK who could actually mix up viable explosives in deadly amounts and who weren't under surveillance. Sensibly, rather than go for a risky caper like trying to penetrate airport security they simply walked onto the Tube, where confined spaces magnified the devices' effect - if not as much as a total structural failure in flight might have. Those men are all now dead, of course, which is what happens to competent suicide bombers - it's a self-correcting problem to some degree. The follow-on 21/7 series of damp squibs indicated that there were several more unknowns willing to die, but that these didn't have the necessary knowhow.
London is still here. Nothing has changed. You can still, any day you want, buy acetone and peroxide, keep trying carefully with small amounts until you learn how to make viable TATP. Then you can make a bomb and take it onto the Tube. If you are willing to die, you can certainly set it off amid dense rush-hour crowds. If you aren't ready to die, you can probably still manage it, to be honest; and if you fail you can try again and again, still being alive - though you'll need to plan carefully to deal with the CCTV.
Hell - as someone who actually can make good TATP, you shouldn't be involved in the operation on the ground at all. Dumb expendable footsoldiers who know nothing should be doing that. But more people means more risk of an informer - which is probably why the average size of terror networks in the UK is just 10 people, according to MI5.