Hi again,
I'm posting this in case it turns out to be your Leonard in 1901 ( the only one that came up) Happy searching

Jan
17, North St, Clapham
Edward M Dignam 14 Widwr Chimney Sweep Own acct Clapham, London, Head Clapham London
Leonard Dignam 9 Clapham, London, Son Clapham London
Mabel Dignam 13 Clapham, London, Daughter Clapham London
Sydney Dignam 8 Clapham, London, Son Clapham London
Source information: RG13/461
Registration district: Wandsworth
Sub-registration district: Clapham
ED, institution, or vessel: 2 Folio: 39 Page: 20 Household schedule number: 134