European Parliament security has come under the spotlight after a post office heist at MEPs' Brussels headquarters netted thieves about 8,000 euro.
Two years ago a man brandishing a pistol stole about 60,000 euro from a branch of the ING bank inside the parliament building.
And last May there was a robbery in the parliament's main canteen.
The post office is also on the premises and the raid occurred in the quiet of Friday afternoon with few MEPs about - and just as 27 EU leaders were meeting for a summit in another building a few hundred yards away.
Belgian police said they believed two men were involved, one of them armed. They took the post office safe after threatening two female staff.
Liberal Democrat MEP Fiona Hall, who arrived at the post office to buy stamps soon after the raid, said: "For an armed robbery to happen - again - inside the European parliament means that the security system here is a complete farce. Something is wrong at the heart of the security system".
Conservative MEP Timothy Kirkhope said: "The European Parliament has been subjected to three significant robberies, potentially involving guns, in two years. This is an absolutely disgraceful situation, not least on a day when there is a good possibility that EU heads of state and governments could be in the building.
"Every time there is an incident, we hear some hollow words about how procedures have been tightened up but it seems they slacken very soon after. We have become increasingly concerned about people in the parliament just wandering around. We have no idea who they are and what they are here for."
Mr Kirkhope added: "The security in the European Parliament has long been well-known as lackadaisical, but this is really ceasing to be a joke. It's about time something were done.
"This time is was a hold-up but how long before someone walks in with a bomb?"