Spain's Prime Minister Mariano Rajoy will on Wednesday, July 26, take the stand as a witness in a major graft trial involving former members of his conservative Popular Party, a first in the country, AFP reports.

Protesters plan to gather in front of the courthouse on the outskirts of Madrid as Rajoy, who is in his second term in power at the helm of a minority government, arrives to take the stand at 10:00 a.m. (0800 GMT).

The court appearance will be embarrassing for Rajoy, who has sought to distance himself from a series of corruption scandals that have for years surrounded his party, in power since 2011.

It will be the first time that an acting prime minister has appeared in court.

Two former premiers -- Felipe Gonzalez, an ex-Socialist leader, and Adolfo Suarez, prime minister during the Spain's transition to democracy -- appeared in court in separate trials but they were no longer in office.

Rajoy, 62, had asked to testify by video-conference but Spain's High Court ruled he must appear in person.

The trial at a court in San Fernando de Henares, near Madrid, centres on a vast kickback scheme that allegedly saw companies shower former PP lawmakers and civil servants with bribes in exchange for contracts.