Data

British dahta, to the extent it exists, may have been due to Australian influence.

I think you should say English rather than British. Dahta would be unsurprising in Scotland.

forgot - appa rah tus

ohwell - other than the free cable car ticket, I would never consider you an old age pensioner!

West Coast Australia - dahta.

This is in greater part due to the Australian practice of articulating in the easiest way possible. ie: trying to achieve minimum mouth movement when speaking.

Ireland, in my 30s - 'dahta'. The vowel is definitely long but more or less the same quality as in 'datta' i.e. not a far back vowel (I think that's the right term?) as in the southern English pronunciation of 'father'.

Though some might think I really pronounce it "daasha" due to the soft Irish intervocalic 't'.

Same vowel in stra(h)ta, same vowel in apparatus.