Non-rhotic accents
A Non-rhotic accent is an accent or dialect in English in which speakers no longer pronounce /r/ in postvocalic environments: when it is immediately after a vowel and not followed by another vowel.
For example, in isolation, a rhotic English speaker pronounces the words hard and butter as /ˈhɑːrd/ and /ˈbʌtər/, but a non-rhotic speaker "drops" or "deletes" the /r/ sound and pronounces them as /ˈhɑːd/ and /ˈbʌtə/.[a] When an r is at the end of a word but the next word begins with a vowel, as in the phrase "better apples," most non-rhotic speakers will pronounce the /r/ in that position (the linking R) since it is followed by a vowel in this case.
For non-rhotic speakers, what was once a vowel, followed by /r/, is now usually realized as a long vowel. That is called compensatory lengthening, which occurs after the elision of a sound. In RP and many other non-rhotic accents card, fern, born are thus pronounced [kɑːd], [fɜːn], [bɔːn] or similar (actual pronunciations vary from accent to accent). That length may be retained in phrases and so car pronounced in isolation is [kɑː], but car owner is [ˈkɑːrəʊnə]. A final schwa usually remains short and so water in isolation is [wɔːtə].
Nafferton, S. (2022, February 15). Yorkshire - Survey of English Dialects - Accents and dialects. British Library - Sounds.
Aveyard, E. (2019). Berliner Lautarchiv: the Wakefield Sample. Transactions of the Yorkshire Dialect Society.
Skandera, P., Burleigh, P. (2011). A Manual of English Phonetics and Phonology, Gunter Narr Verlag.