In Europe, war broke out between Britain and France in 1803. The war prevented merchant ships from Holland and Britain to sail to Guyana and the planters found problems in obtaining supplies. The planters in turn were unable to export their products and to pay their instalments on mortgages held in British and Dutch banks. By this time investment by British banks in the Guyanese sugar plantations was very high but they faced a serious problem of the devaluation of their stocks if shipping was not resumed. The British bankers felt that only the resumption of British control of Guyana could save their investment and this view was supported by the planters in Guyana.

The British invasion of Guyana occurred on the 17 September 1803 and the soldiers were joyously welcomed by the planters. The capitulation was signed on the following day (in Stabroek) by Commodore Samuel Hood and Lieutenant-General William Grinfield on the British side and Governor Meerteens and some of his councillors for the Dutch. But Grinfield, the commander of the British forces, immediately faced difficulties presented by the Court of Policy (in Demerara-Essequibo) which had a high representation of planters of Dutch origin. By the terms of the surrender of the Dutch colonies (Demerara-Essequibo and Berbice) to the British, it was agreed that no new establishment would be introduced without the approval of the Court of Policy. As a result, when the British decided to establish a customs house and income tax, the Court of Policy objected on the grounds that these were "new establishments". Nevertheless, the British imposed these over the objections of the Court of Policy.

Within a month, the British appointed a Governor, Lt. Colonel Nicholson, who oversaw the immediate administration of the colonies until separate Governors were named for Berbice and Essequibo-Demerara.

In 1812 Major-General Hugh Lyle Carmichael was appointed Governor of Demerara-Essequibo. In May of the same year he changed the name of Stabroek to George Town after the heir to the British throne, who later became George IV. Then in October, on behalf of the Government, he purchased an area of land in Cummingsburg for a Parade Ground. Towards the end of the century, half of it was used for the development of the Promenade Gardens while the other half remained as the Parade Ground.

Up to this time Dutch was still the official language of the courts but Carmichael modified this by ordering that all legal documents must now be written in both English and Dutch.

The Dutch planters who held influence in the Court of Policy and the College of Keizers (part of the combined Court of Policy) offered stiff opposition to Carmichael's administration. The College of Keizers in particular was seen as an exclusive domain of the Dutch planters who always nominated one of their own when a vacancy occurred. Without receiving approval from Britain, Carmichael abolished this body and handed over its duties to the Financial Representatives (in the Court of Policy).

During the same year, the United States of America joined the war on the side of France, and in September American warships blockaded Georgetown. A British force stationed in Georgetown launched a successful attack on the Americans and drove them away from Guyana's shores. However, in February 1813, a British patrol ship, the HMS Hornet was sunk off Mahaica after a battle with an American warship, the Peacock.

During the period 1803-1814, English planters who owned three-quarters of the property in the colonies faced severe economic hardships on account of crop failures. These planters were faced with great difficulties in meeting payments on mortgages held mainly by Dutch and English investors. By existing Dutch law, plantations experiencing such difficulties were handed over to Dutch administrators who could put them up for sale and then purchase them at any price. The English planters were therefore at the mercy of the Dutch and could obtain little justice from the Court of Justice which was controlled by Dutch lawyers. At one time seven members of the Court were administrating 60 indebted estates.

The English planters felt that the situation could not improve unless the colonies were formally ceded to Britain. This finally occurred in 1814 when a Convention held in London confirmed the capture of the colonies. The Convention decided that Britain would keep the colonies along with the Cape of Good Hope (South Africa) on the condition that Britain paid one million pounds to Sweden (which were debts owed by Holland to Sweden) and also two million pounds to Holland itself. This decision was confirmed by the Treaty of Paris in 1815.

With final British control established, a proclamation was issued which settled the debt situation with the Dutch and English investors. Under an arrangement, the Dutch holders of mortgages on English-owned plantations agreed to suspend their claims in return for a new mortgage for the whole amount owed, plus interest.

As has been mentioned, separate Governors were appointed for Essequibo-Demerara and Berbice, but as the years progressed, the Governor of the former assisted in the administration of the latter when its Governor was absent. Gradually, the opinion that the colonies should be united became popular, and it was no surprise when King William IV on 4 March 1831 issued a Commission which united Essequibo-Demerara and Berbice as the Colony of British Guiana. Sir Benjamin D'Urban, who was serving as Governor of Essequibo-Demerara was appointed the first Governor of the united colony. In 1838, for administrative purposes, the united colony was divided into the three counties of Essequibo, Demerara and Berbice.

At first, the unification brought about some dissatisfaction among Berbice planters who felt that they did not have sufficient representation in the united Court of Policy. They had hoped for a reduction in taxation, but this did not happen.