Hi Jeff
Until the early 1990's, all major and most smaller Philatelic Exhibitions in the UK offered show souvenirs to the visiting public.
These were either sold for a small fee or given away free. Many were used on cover alongside postage stamps.
The same happened in the USA,Canada,Australia and so on.
The labels or sheets produced were often a celebration of some kind even if the Exhibition was not.
What you have are labels that could be purchased in a sheet of 12 for 1/6 [7˝p]on entry to the 1960 London International. The labels celebrate the Tercentenary of the appointment of Colonel Henry Bishop as the UK's first Postmaster General.[1660-1663].
Perf 11 in Orange-Red and Black.
Two other sheets exist in Imperf and part Imperf condition.
Each label shows a different Bishop Mark which were used in the UK and overseas possessions.

Londonbus1