Perhaps someone can confirm whether Jet2 do "packs-off" take offs on their 738's. If they do, then that would put paid to the water vapour theory (unless they run the packs/APU for takeoff).
Water vapour tends to evaporate almost instantly as it enters the cabin - it doesn't "fill" the cabin! Additionally the conditions hardly seem conducive to water vapour (GLA at 7am in Oct is not the same as a muggy IBZ at 32C in summer!)
It must that've been something pretty spectacular for the CC to make the call - but if in doubt....... no doubt.
Last edited by A4; 24th Oct 2012 at 07:28.