"...Flashman's adventures take him the length of the 1840s to 1860s..."
That covers about 6 or 7 of the books (but Flash Harry runs well past the 1860s), I assume the TV pieces will be based on Flashman, F at the Charge and F & the Great Game - although, as they are also making 'Prisoner of Zenda'*, it's possible they will go for 'Royal Flash', while they have access to the locations/sets.

I look forward to seeing them.


* There was a rumour, some time back, that there was a plan to produce a version of @Prisoner of Zenda' with Sean Bean in the lead role - strange, I never saw P of Z as a comedy (well, it would be impossible to take him seriously as Rudolf Rassendyll or King Rudolf of Ruritania)