Anncook is not going to help you in British accent, I am a trainer and I train on any British accent including R.P,Scottish, Cockney, Welsh and, Irish.
It is easy for Indians to develop neutral accent however, If one wants to develop an R.P accent(BBC accent) then it can be possible too. Some people wrongly refer R.P accent to neutral but it’s so not true. I live in delhi and I do provide lessons on the phone for remote students.
Watch more of British movies if U can’t find a good Institute.