hello deep singh,
as per my last information, PR or NON-PR, its same for all, transit visa is not needed for connecting flights.
i came via heathrow early this year, did not need transit visa, no matter how many stops/countries your flight stops en route, you do not need visa if you do not leave the airport, i had same experience for amsterdam and zurich, the passenger area of any international airport is considered international travel zone so no visa is needed for flight change or stop-over of few hours,( i m not sure of much longer stopover periods/ like days), and one more thing that i found out... at heathrow there are very good large sofa seats near terminal A7 with play area for children, anyone who has more than 2-3 hours stay can go and have a comfortable rest/short nap there.. hope i was helpful.. god bless.