The United Kingdom’s domestic security service, MI5, warned politicians and their staff that they are being targeted by spies from China, Russia and Iran in efforts geared toward undermining British democracy.

The warning, which follows the collapse of an espionage case that has put Prime Minister Keir Starmer’s handling of national security under scrutiny, comes in new guidance published Monday for people working in British politics about how to counter "espionage and foreign interference.”

"The U.K. is a target of long-term strategic foreign interference and espionage from elements of the Russian, Chinese and Iranian states which, in different ways, seek to further their economic and strategic interests and cause harm to our democratic institutions,” according to the advice.

The document comes just weeks after a high-profile espionage case in which two men were accused of spying for China fell apart, sparking criticism of the government’s handling of the case and Starmer’s wider policy toward Beijing, with which he has sought to improve diplomatic ties since entering office last year.

Separately, Nathan Gill — a former Welsh leader of Nigel Farage’s populist right-wing Reform U.K. party — pleaded guilty last month to taking bribes in exchange for making statements in favor of Russia.

In Monday’s rare public intervention, MI5 warned politicians and political staff to look out for what it called "threat actors” seeking to elicit information from them, cultivate long-term and deep relationships with them or blackmail them.

The security service said foreign actors may use a range of methods, from dishonest online approaches such as acting as recruiters, to hacks and cyber attacks, in order to recruit assets and obtain information.

Foreign states may use financial donations to politicians purporting to come from U.K. nationals, or indirectly give money to projects in their local area, with the aim of influencing their decisions, the guidance said.

MI5 urged politicians to "keep track of odd social interactions” and be wary of "overt flattery,” as well as conduct due diligence on new contacts, secure their digital information and enhance their overseas security.

"What might begin as an apparently genuine interaction can transition into something more malign,” the guidance said. "It’s important you remain alert and trust your instincts. If something doesn’t feel right, report it to your security team promptly.”

Speaking in parliament on Monday evening, security minister Dan Jarvis said the new guidance was part of the government’s response to the aborted spying case as it attempted to demonstrate its commitment to national security.

Jarvis denied allegations that Starmer’s administration deliberately hampered the case to protect diplomatic relations with Beijing. "Suggestions that the government concealed evidence, withdrew witnesses or restricted the ability of witnesses to draw on particular bits of evidence are all untrue,” he said.

In remarks accompanying the advice, MI5 director-general Ken McCallum said, "Everyone reading this guidance cares deeply about the role they play in U.K. democracy. Take action today to protect it — and yourself.”