More sleuthing:
Alexander Sebastian LINDSAY (b 1940), heir presumptive, is listed on
thepeerage.com as resident in Carshalton in 2003 (source Debrett's 2003).
Electoral Roll lookups on
192.com indicate he lived with a Deidre A LINDSAY 2002-2007 in Carshalton, then 2007-present in Sutton.
Ancestry Electoral Roll lookups have him living with a Deidre A LINDSAY in 1966-68 also, so this is very likely to be his wife.
Marriage lookup gives a 1962 Q3 marriage to a Deidre A DICKSON in 1962 Oxford.
Three possible children soon after:
Simon A LINDSAY, born 1963 Q2, Wandsworth
Emma S S LINDSAY, born 1965 Q1, Surrey Mid Eastern
Thomas Peter LINDSAY, born 1967 Q3, Sutton
There are other LINDSAY/DICKSON children born later, but there is also another LINDSAY/DICKSON marriage in 1967 Q1. Difficult to be sure of where these belong.
This does give us 2 more heirs (if true), but actually no younger than the youngest brother of Alexander who was also born 1967.