HMS Demerara was the French privateer Cosmopoli, launched, captured, and purchased in 1806.

The inhabitants of Demerara purchased Cosmopoli on 9 February 1806,[2] and presented her to the Royal Navy.

Commander William Maude commissioned Demerara in the Leeward Islands and she was in service by 17 March 1806.

[3] Commander William Shepheard replaced him.Demerara captured a Spanish privateer and completely suppressed the depredations of the enemy’s row-boats from the Oronoco river, which earned him the thanks and a gift from the British merchants there.

In 1847 the Admiralty awarded the surviving claimants from the campaign the Naval General Service Medal with clasp "Martinique".