I see that there is a death registered for Thomas Spark English in the March quarter of 1989 in Cambridge, born 15 Feb 1919, reference vol 9 page 914.
If this is the individual you are interested in, then you could also order the death certificate, if you wished, which should give you the place of birth, just as confirmation.
Does your uncle remember what his father or grandfather did for a living?
You have done the right thing by ordering the birth certificate for Thomas, as this should give you a solid lead with the names of the parents. Perhaps you could post again to let us know what the birth certificate said, as people may be able to help at that point?
www.freebmd.org.uk shows the following English children with a mother’s maiden name of Pearson being born in the Durham registration district:
Edith Dec q 1916
Thomas S Mar q 1919
Elizabeth A Jun q 1921
These dates could suggest that the father was absent during World War 1 (or just that the family moved around). Does your uncle recall whether his father mentioned his grandfather serving in WW1?