Berenice - you are right on Hugh. There were 10 siblings - eldest born in Scotland, youngest in Warley (Smethwick) - all the others were born in Middlesbrough and that is what its says time and time again on census returns including the 1911 one for Philip which he filled in himself. If you start looking for birth registrations for the elder Middlesbrough ones they are all registered in Stockton. Now Stockton-on-Tees and Middlesbrough face one another across the Tees. One would assume that the border between the two towns would be the Tees and the same would go for the border between the Reg districts but it would appear that at one time life was not that simple. So why could you not find the birth of a Philip John Reid registered in Stockton because on the registration form they have spelt his surname incorrectly as "Ried".
You can find Philip's probate which tells you he died on 20th April 1932 at Whitehill, Woburn, Marlow, Bucks - so other side of M40 from Wycombe not that the M40 would have been there then. Definitely him as his youngest sister is named as executor.
The naming of two of their sisters is interesting - one was christened Millicent Fawcett Reid and another Octable Turquet Reid.
This gives you a flavour of their larger than life father, Sir Hugh Gilzean Reid. He was also a Liberal MP for a couple of years, had Mark Twain stay with him when he was looking for some solitude to finish off one of his books, and did some good works relating to the Belgian Congo for which he received the Order of Leopold (which considering what is now recognised about King Leopold of Belgium is a bit of a dubious distinction to have received). He has a Wikipedia entry.