Lancaster using flare

[FlKp21_Tabo]

I am working on the circumstances of the crash of a Lancaster bomber going to Turin. Actually this crew had some problem with at least one engine just before crossing the Alps, they were lost but did not jettisoned the bomb load for an unknown reason.

Eyewitnesses stated that the plane launched a flare just before crashing in a mountain slope.

In my knowledge, apart from the PFF squadrons, the Lancasters were equipped with only one flare used for taking the picture of their results on target.

I would like to know :
- was the use of this flare automatic (when opening the bomb bay for example) or could it be activated at will by the bomb aimer (in this case, to light the country side, in order to see where they were)
- when jetttisonning the bomb load, was it possible to selection what to launch or was there and “automatic order” (first le SBCs then the HBs for example)

Thanks for your help !