The firm, which rents out and sells formal menswear, sources its antique silk top hats from around the world. These silk versions, which it sells for in excess of £500, are rarer due to the demise of commercial production following the closure of a factory in Lyon in the 1960s that had produced the fabric.
The scarcity of these original silk hats, as opposed to the more recent design of grey felt, has boosted turnover and Oliver Brown predicts sales will hit £1m for the month to June - up 25% from the previous year.
The company, which has a shop on Lower Sloane Street in London, was appointed the official licensee to Royal Ascot in 2017.
Owner Kristian Ferner Robson said its customer base has widened to include buyers from Europe, the United Arab Emirates and Australia.
Royal Ascot 2018 concludes on Saturday, 23 June.