The UK citizenship authority accepts most major accredited english language certifications and or a university degree as proof of english language proficiency. The only tests are for lay of the land/law/society, not language proficiency.
Not sure what your sources are, but as part of UK Citizen application, you absolutely have to do English language proficiency tests in some circumstances. The Pearson test is one of the recognised tests.
In addition to my self having gone through the Citizenship process recently. Additionally several native nationalities have an exception: https://www.gov.uk/english-language/exemptions