The best scenario for the British Empire is to keep the Revolutionary War in the 13 colonies to happened and to give them a dominion status by 1800 to satisfy the demands of the colonists of more representation.
With the collapse of the Spanish Empire, Great Britain could grab their some colonies such as the entire Viceroyality of Rio de la Plata, Cuba, Philippines, and Puerto Rico which are most stategic colonies of the crumbling Spanish Empire.
Also, British support the Taiping rebellion to overthrow the Qing Dynasty. If they could overthrow them, the British could get the large chunk of China.