There’s a William 42 & Agnes Best 40 in Finchley in 1891. Right ages but says both born London 
Deaths Mar 1896
Best Agnes aged 47 Barnet 3a 153
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Marriages Mar 1898
Best William Thomas Salisbury 5a 249
Soper Letitia Jane Salisbury 5a 249 Image on Ancestry
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1901 at same address as 1891
1911 census still at same address
William born 1852 Tisbury
Letitia born Salisbury
Letitia born Finchley
BEST, LETITIA MARY mmn SOPER
GRO Reference: 1908 D Quarter in BARNET Volume 03A Page 401
SS
easily found in 1921 census.
Deaths Sep 1935
Best William T 84 Barnet 3a 466
Deaths Mar 1937
Best Letitia J 70 Barnet 3a 819