MEPs were light-hearted when they met in Brussels
The European Parliament building in Strasbourg which had to be abandoned by MEPs when a ceiling collapsed, is still not safe to use, officials have ruled.
It means that for a second month, a session of the parliament will have to be held in Brussels.
Many MEPs have stepped up their calls to scrap the two-seat system and base the parliament permanently in Brussels.
Critics says moving 785 MEPs and their staff between the two sites is expensive and bad for the environment.
However, supporters of the Strasbourg base say the city is symbolically important, sitting on the border of former European foes France and Germany.
A huge section of the suspended ceiling collapsed on 7 August, fortunately while the chamber was empty.
The parliament, which has to meet 12 times a year, held its first ever full plenary session in Brussels this week - a move warmly welcomed by many MEPs.
Since then the ceiling has been repaired but a full inspection of the building has revealed other areas that need safety improvements.
Now the parliament's full session from 22-25 September will also have to be held in Brussels.
Part of the ceiling caved in while MEPs were on holiday
"It has not been possible, despite the efforts of parliament's services and the assistance of the French authorities, to remedy in time the situation... which prevents the institution from meeting all the conditions for safe use of the Strasbourg site," a parliamentary statement said.
British Conservative MEPs are calling on Prime Minister Gordon Brown to make a stand in the EU's Council of Ministers and demand the two-seat operation be scrapped.
Philip Bushill-Matthews MEP, European Conservative leader, said there was now no viable argument for the parliament's monthly move to Strasbourg.
"We have always said there is no need to decamp to Strasbourg, and this week has underlined the point," he said.
"For example, following the EU Brussels summit on Monday, the French foreign minister was able to report back to MEPs instantly because we were also in Brussels. If we had been in Strasbourg, we would have been out of the loop.
"The desire to scrap the parliament's two-seat operation is shared by most nationalities and all political persuasions. It is one of the few issues that unites almost all MEPs."
Gary Titley, Labour's Leader in the European Parliament, said: "It is time to break with tradition and to make Brussels the only seat of the European Parliament.
"As long as we have to travel to Strasbourg, people will rightly say that the EU is wasting money - Strasbourg is a waste of taxpayers money," he said.
"Labour MEPs are opposed to the Strasbourg travelling circus. It is time for national governments to bite the bullet and end the wasteful monthly commute and to give the European Parliament a long overdue permanent home in Brussels."
The Labour group has started an online petition calling for the parliament to be based in Brussels.
The annual cost of shuttling between Strasbourg and Brussels is estimated at 203m euros (£160m). The Green Party says it produces about 20,000 tons of carbon dioxide annually.