The 1901 census has 2 Grosvenor Clarke's:
#1: Age 7 born Hants Bishopstoke, census place was Eastleigh Southhampton
#2: Age 7 born Birmingham, census place was Edgbaston Warwick.
Firstbrook age 7 was also at #2.
I didn't look at the actual census entries, which may or may not include his middle name.