His father, Ernest Samuel Garrison – a cabinet maker born in Hopewell, Hanover – and mother, Albertha Adassa Garrison, a school teacher born in Somerset, St Andrew, migrated to Britain in 1952 and 1953 respectively, and Len joined them there in west London in 1954 shortly before the birth of the first of his British siblings, sister Janet in May 1954.

Its aim was to give black children a sense of identity and belonging to be proud of, and one that could be traced back to their African roots.

Garrison saw ACER as an archive of Black history from which educational material could be developed for school children of all ages and abilities.

He campaigned for two years with the Inner London Education Authority (ILEA) and others for the funding and resources until 1977, when the ACER project was launched with Garrison as director.

ACER's legacy can be seen today in black history being part of the mainstream British educational curriculum[6] and its work has inspired the Dutch to develop similar multi-cultural learning.

[7] Garrison believed that "collecting and structuring the fragmented evidence of the Black past in Britain as well as in the Caribbean and Africa is a monumental task, but it is a major agenda item in [the] last decade of the 20th century [to create a] better basis for achieving a fully multicultural British society"[8] To this end he co-founded the Black Cultural Archives (BCA) in 1981 and became a trustee.

The BCA won funding of £5million in 2010, and having been based in Kennington, moved back to Brixton to become the UK's first national black heritage centre.