triacetone triperoxide is a solid, not a liquid. It can be manufactured by combining various solutions on board the aeroplane, but this is quite tricky, and prone to failure. TATP is used as a detonation fuse to set off other explosives--indeed, Richard Reid's shoes used a tatp detonator to...
Probably standard operating procedure. Remember, the Soviets didn't try to coddle their political dissidents. Unlike the FBI, they had no pesky qualms about applying electrodes to sensitive portions of the perp's anatomy... They knew how to deal with civil rights movements in Russia. And morals...
Al Quada and allied groups have been tinkering with liquid explosives for some time (elements of hezbollah used it in the early 1980s). It's the kind of thing that appears in internet bomb handbooks. Intelligently evaluating risks is important for combatting terrorism.
It's probably triacetone triperoxide. One recipe for acetone peroxide bombs (found on the internet-- where else) involves Hydrogen Peroxide, paint thinner and sulfuric acid. Other possibilities are discussed here
It could imply that the threat still exists, but the cost benefit of keeping the restrictions in place wasn't justified. For all I know, it could have been a publicity stunt designed to promote the British anti-terrorism bill.