Is /ɜː/ realized as schwa [ə] in British English?

I have noticed that the vowel /ɜː/ (as in the RP pronunciation of "BIRD") sounds the same as the schwa [ə] (as in the pronunciation of "BUTTER" in RP). I assume the BIRD vowel is a bit longer than [ə] and occurs in stressed syllables and has the same quality as [ə]:

• /ɜː/ = [əː]

And looking the word BIRD up in Lexico added to my doubts, Lexico gives /bəːd/ (Cambridge gives /bɜːd/, BTW).

My question is: Is /ɜː/ realized as [əː] in modern RP?

Solution 1:

You might as well consider them to have the same sound quality; many British English speakers use the same vowel sound for them (while others use slightly different vowel sounds).

They are not the same phoneme, and people's pronunciations of phonemes vary, so you can't say there is only one "correct" realization of /ɜː/ in modern RP. But they are generally similar vowel sounds, and lots of speakers do pronounce them with the same vowel.

In his 1982 book Accents of English, John Wells (a very highly respected former professor of phonetics at University College London) says that /ɜː/ is "a relatively long unrounded mid central vocoid, [əː]." See this blog entry for the quote. So some experts consider them to be the same vowel sound.