Pronunciation of final T sounds in English

Disclaimer:
When referring to British English, I am referring to non-colloquialized British English. The pronunciation, as it is intended in a formal and correct sense. Given the enormous and varying accents across the United Kingdom, it is impossible to give an accurate assessment; it would require a thesis. I am using American English and British English; within the least colloquialized forms. There are exceptions to all the rules.
As for Australian English, it was originally influenced by the British, but now is equally influenced by American English; so makes an interesting study of a hybrid of the two. (my opinion and observation)

I am trying to best answer a question that has an encyclopedia of answers and exceptions.

The sound of a t at the beginning of a sentence is an aspirated t; which is used in both American and British English.

A final t becoming a de-aspirated is a glottal stop, this is used in both American and British English.

A flap is not used in British English.

There are varying colloquial pronunciations within both American and British English. Living in Australia, we are influenced by an interesting mixture of American and British English. As a general rule, the extent to which a person uses non-colloquialized British English, is an indicator of social class and education. The more British, the higher perception of social class. A good example of this being in the use of tapping. The pronunciation of potato with two t sounds as opposed to potado.

I have provided extensive quotes.

Tapping of / t / In American English, if a /t/ sound is between two vowels, and the second vowel is not stressed, the /t/ can be pronounced very quickly, and made voiced so that it is like a brief /d/ or the r-sound of certain languages. Technically, the sound is a ‘tap’, and can be symbolised by /t̬/. So Americans can pronounce potato as /pəˈteɪt̬oʊ/, tapping the second /t/ in the word (but not the first, because of the stress). British speakers don’t generally do this. The conditions for tapping also arise very frequently when words are put together, as in not only, what I, etc. In this case it doesn’t matter whether the following vowel is stressed or not, and even British speakers can use taps in this situation, though they sound rather casual.

The glottal stop In both British and American varieties of English, a /t/ which comes at the end of a word or syllable can often be pronounced as a glottal stop /ʔ/ (a silent gap produced by holding one’s breath briefly) instead of a /t/. For this to happen, the next sound must not be a vowel or a syllabic /l/. So football can be /ˈfʊʔbɔːl/ instead of /ˈfʊtbɔːl/, and button can be /ˈbʌʔn/ instead of /ˈbʌtn/. But a glottal stop would not be used for the /t/ sounds in bottle or better because of the sounds which come afterwards.

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British English, as represented by Received Pronunciation (RP)...

American English, as represented by General American (GA)...

As an aspirated sound [th ], when it is the first sound of a word, as in tempting["t h emptI6], or in an inner and stressed position, as in potential [p@"t h enSl].

As an de-aspirated sound [t], when the syllable does not carry the stress, as in the second t in tempting["t h emptI6], or after [s] as in stop[stA:p], or at the ends of syllables as in pet[pet], or patsy["pætsi].

As a flapped sound [R], the most distinguishing allophone, which consists of pronouncing an alveolar flap instead of the plosive dental [th ] or de-aspirated [t]. This change occurs when t is at an intervocalic position, the first vowel being stressed, as in water["wO:t@r]. This phenomenon also applies when words are linked together in a full prosodic unit, as in the sentence What is this?["w2RIz"ðIz] when uttered it in colloquial register.

As a glottal stop [P]. A glottal stop is a voiceless sound produced by the obstruction of the airflow in the vocal tract. The glottis is the organ that actually prevents the air from passing through the vocal tract. The glottal stop substitutes the de-aspirated [t] sound at the end of words, as in put[puP] or report[rI"pO:rP], and also in the presence of a stressed syllable followed by patterns [t+vowel+n] or [tn], as in button["b2Pn], or continent["kA:nPIn@nt].

As a glottalized stop [tP ]. In a glottalized [tP ] the stop [t] and the glottal stop [P] are produced at the same time. For its production, this allophone follows the same rules as the glottal stop does. Example where this sound can be found are mutton["m2t Pn], or curtain["k3:rtPn].

The sound [t] could be completely omitted in some circumstances. In the presence of the pattern formed by a stressed vowel followed by [nt], sound [t] is not pronounced in some varieties of GA. Thus, we can hear winter["wIn@] or center["sen@r].

Both GA and RP have aspirated and de-aspirated [t] sounds, which, in a formal or simply careful enunciation, are the only two sounds corresponding to stop [t]. In colloquial and other registers, the other allophones may appear. In the RP the flap [t] is never used, but instead it is pronounced as a de-aspirated [t] or as a glottalized [t] (see [AE92] for a description of this sound). Glottal stops are common in both varieties of English and follow similar rules in general. The omission of the sound [t] in RP can also be found.

British and American English Pronunciation Differences Paco G´omez