Brian Stott is a well-known power system guru. I don't know the reason behind to find out this thesis about 50 years ago. There are many papers out there in the literature that improves the power flow solutions. You can easily find those papers in the literature. 

this thesis does not exist in the Internet

And in my personal opinion there is no need to know it will not benefit from it because it is very old

 https://scholar.google.com/scholar?q=Stott%20B%20%281971%29%20Load%20flow%20for%20AC%20and%20integrated%20AC%E2%80%93DC%20systems%2C%20Ph.D.%20Thesis%2C%20University%20of%20Manchester

https://books.google.com.ng/books?id=Y2FW94TtaQ8C&pg=PA277&lpg=PA277&dq=%E2%80%98Load+Flow+For+AC+and+Integrated+ACDC+Systems%E2%80%99,+Ph.D+Thesis+University+of+Manchester,+(1971)%5D&source=bl&ots=BshPt68Vs5&sig=mXAgVLyk8Wgl1PeJEx-2dZ5ZF8A&hl=en&sa=X&ved=0ahUKEwjT7IHV1JfVAhUhCMAKHUgQDBEQ6AEIJDAA#v=onepage&q=%E2%80%98Load%20Flow%20For%20AC%20and%20Integrated%20ACDC%20Systems%E2%80%99%2C%20Ph.D%20Thesis%20University%20of%20Manchester%2C%20(1971)%5D&f=false.

check the site. the book is available but not on PDF