The two governments announced their agreement after Spanish Foreign Minister Jose Manuel Garcia-Margallo met with British Foreign Secretary William Hague in London.
The ambitious plan was seen by analysts as a response to Spanish frustration over Argentina's confiscation of Repsol's local energy company YPF and Bolivia's nationalization of Red Electrica de Espana's local unit.
Spain is reported content with Bolivian assurances that Red Electrica will be adequately compensated but is battling to keep its temper over Argentine actions.
On the government's bidding Spanish King Juan Carlos intervened to resolve differences but was rebuffed by Argentine President Cristina Fernandez de Kirchner, who spearheaded a swift takeover of YPF Repsol with legislative support from the national congress. No compensation was offered despite repeated Spanish demands.
Britain's support to the planned pooling of political clout, such as it may exist, follows what London sees as Argentine government-backed harassment of its South Atlantic territory, the Falkland Islands.
Argentina invaded the islands in 1982 but was repulsed by Britain in a 74-day conflict that caused 907 deaths.
Argentina is pursuing an international campaign to force Britain into talks over Falklands sovereignty, which Argentina disputes and claims as its territory.
It was unclear if Garcia-Margallo's gesture signaled the start of a strategic alliance between Britain and Spain in Latin America or was part of rhetoric aimed at Buenos Aires.
"We have agreed on defending and mutually protecting each other in Latin America," Garcia-Margallo said.
He said the two countries will "join forces and keep talking over their policies in Latin America, defending judicial security and protecting the interests of Spanish and British companies whenever they are under attack."
Britain has been angered by Argentine blockade of shipping to and from the Falklands, Argentine sanctions and threats of lawsuits against companies exploring offshore for oil and a government-led call to Argentine businesses to boycott British goods.
Argentina is facing international condemnation and is at risk of losing preferential trade with Europe and the United States in separate U.S. and EU actions.
The planned British-Spanish collaboration contrasted with recent heated arguments between the two countries over the status of the British territory of Gibraltar, which has been at the center of negotiations over "shared sovereignty." Britain is a major creditor of Spain, its current financial restructuring a source of major worries for British banks and other investors.
It also sees Spain as a valuable interlocutor in Latin America because of its historical links, even as they don't always work to Madrid's advantage.