Johnston joined the
Metropolitan Police in 1965 and served as Staff Officer to former Metropolitan Police Commissioner
Peter Imbert. In 1982, he graduated from
London School of Economics with a first in
Social Administration. Having completed the
Senior Command Course at Bramshill, Johnston moved to
Kent Constabulary in 1989, where he served as
Assistant Chief Constable in charge of first Administration and Supply, and then Operations, before moving back to the Metropolitan Police in 1992 as a
Deputy Assistant Commissioner. In 1994, he was appointed
Assistant Commissioner for the South East London area, but later became Assistant Commissioner with responsibility for Territorial Policing. In September 2009, Johnston retired from the British Transport Police and was succeeded by Andrew Trotter. Johnston came to media attention having given evidence before the enquiry and following the publication of the
Macpherson Report into the murder of
Stephen Lawrence. On behalf of the Metropolitan Police, Johnston apologised to the Lawrence family for institutionalised racism, but argued that race can legitimately be used by police as a basis for stop and search. Johnston reiterated this argument in the aftermath of the
London Tube bombings in 2005. Johnston had been mooted as the next
Commissioner of the Metropolitan Police after the retirement of
Sir John Stevens in 2005. Stevens had described Johnston as a "substantial figure" at the Met, and noted that following his departure for British Transport Police Johnston was missed. The role of Commissioner went to
Sir Ian Blair. ==Later life==