Pp, you're right to suggest that a good standards of oral and written English are needed to complete a PhD in the UK.
However, you should not make the mistake of judging peoples fluency from the posts that they place on this forum. It offers no facility for users to correct any mistakes once they have posted them, consequently most threads on the forum contain any number of mistakes.
Rasel, presumably you have already passed the required English language exams for entrance to a UK university. Once you are living and working in the UK your English will improve considerably.