Eleven years since opening his restaurant in the shadow of the European commission’s vast Berlaymont headquarters in Brussels, Philippe Weiner can safely boast that the Meet Meat Steak and Wine House is a firm favourite of the better-fed Eurocrat.

Sharp-suited diplomats and officials flock to its minimalist dining room for lunch and dinner. The president of the European council, Donald Tusk, and his team have been known to enjoy the kitchen’s meat offerings, best served à point or saignant.

But on Tuesday, between ushering guests to their tables, Weiner, 39, was fighting off claims that his establishment had become a haunt for another, rather more sinister, type of diplomatic envoy.

The EU’s diplomatic and foreign wing, the European External Action Service (EEAS), alerted member states’ embassies last week to the presence of about 250 Chinese and 200 Russian spies said to be roaming the embassy-lined streets of the Belgian capital.

The missive suggested diplomats should avoid a popular steakhouse and cafe within walking distance of the commission headquarters, according to a report in the German newspaper Die Welt.

“I’m the only steakhouse around here, it has to be me,” admitted a flabbergasted Weiner when visited during a busy lunchtime. “It is nonsense, but, OK, I will talk to you for five minutes. Then I have to call Putin.”

There is little doubt that Brussels is keenly watched by the world’s intelligence agencies. It hosts both the EU’s institutions and Nato, the western military alliance.

In 2003, bugging devices were found hidden in the translators’ booths in the European council’s Justus Lipsius building and in 2014 the European parliament posted security guards outside its more sensitive meetings because Russian agents were believed to have infiltrated discussions.

Last summer during the Brexit talks the EU’s deputy chief negotiator, Sabine Weyand, suggested MI6 could be up to no good. And the head of Austria’s domestic intelligence agency said in June that “Brussels has now overtaken Vienna” in terms of the sheer number of agents from the “so-called intelligence services from outside the EU”.

Weiner said he did not doubt his patrons were the keepers of many secrets and that there were secret agents on the streets. “I have played golf twice with the US ambassador, the one that was friends with Bush, and they had 650 staff in the embassy – they weren’t all doing passports,” he said.

Staff at work in Meet Meat restaurant in the heart of the European Union district in Brussels. Photograph: Thierry Monasse/Getty Images

“We have commissioners every day in here, and Donald Tusk two or three times with his team,” Weiner said. “But people don’t come here to work. You see him over there? With the white shirt? He is in here everyday. He’s not working. Not with two glasses of wine.”

Pointing to his handwritten book of reservations, Weiner said: “I have got all the emails and they are all Europa emails [from the EU institutions] not hotmail or google mail. I never see any laptops out. Do you see anyone with pencils out? I don’t believe it. It is just impossible.”

He added: “You can check under the tables and you won’t find microphones – chewing gum, maybe.”

Weiner said his restaurant had been swept by security officers before a VIP visit. “But that isn’t for bugs, more for explosives.”

“These people aren’t stupid,” he said. “To work in the European commission you have to be very smart, have diplomas and everything. People aren’t spilling secrets. It is a noisy restaurant anyway, you wouldn’t hear anything on the next table.”

An EU diplomatic source attached to an embassy confirmed that a note had been sent to diplomats with regard to the threat of espionage.

A spokesman for the EEAS said: “The EEAS does not comment on issues relating to leaked information. The EEAS, together with other EU institutions and the member states, continuously evaluates the threats to its security, including information security.

“The EEAS has measures in place to ensure the protection of its information. These measures are not subject to public discussion.”