Various stories link it to the second Earl Grey, who was British prime minister between 1830 and 1834 and largely responsible for the Great Reform Act of 1832 as well as removing the monopoly of the East India Company on importing tea from China…. The etymological problem for the OED was that the first example of the term Earl Grey tea it had on record was dated 1929….
The story took a surprising twist when researchers on the Foods of England site found that Charlton and Co had advertised a tea in 1867 as the rather expensive “celebrated Grey mixture”, with no reference to any aristocratic connection, though it did boast of its “most distinguished patronage”. Might the business have added a noble association later on as a marketing ploy, one that was to be copied by others? It could well have done. Victorian advertisers weren’t renowned for their strict adherence to truth.
There’s more, including a discussion of the disreputable adulteration of tea with bergamot. As Quinion says, “at times a search for the provenance of a term turns into an intriguing detective story with an unexpected dénouement.” (Via Etymolist.)