The British obviously speaks better English as the Oxford English Dictionary is the standard for correct English.
However, correct English has varieties as we all speak a version of English. The language is the most populous Lang that is sending many languages into extinction. The reason Nigerians or any other country speaks English the way they do isn’t because they’re too lazy to twist their tongues or anything but because English has always been a second language to them and as such will most likely speak and learn English the way they’re exposed to it, the mother tongue always gets in the way, which is why we easily replace or substitute sounds that are too difficult to pronounce or strange sounds
(Sounds in English but ain’t available in native lan) with the once similar in their mother tongue. The same way we have Jamaican, Ghanaian, American, versions of English language.
It ain’t our fault, it just ain’t in our blood. Thank God for modernization and exposure to technology some of us can now break free and learn to pronounce words/sounds the right way.