Wembley: Building of the new Wembley Stadium has suffered a fresh setback after defects were detected in its sewer pipes, it was reported today.

Ground movement led to the pipes buckling beneath the £757million site in north London. Engineering sources told The Sun that work to rectify the problems at the 90,000-seater stadium could take up to eight months.

A worker on the site told the newspaper: "Pipes buckled because the ground around them had moved. Water and waste from flushed toilets would have backed up and overflowed if no repairs were done.

"On match day, when tens of thousands of people use the toilets at the same time, that just doesn't bear thinking about."

Defects with the sewer pipes are the latest setback to dog the Wembley project, following the collapse of a roof rafter this week which led to thousands of workers being sent home.

Steve Kelly, of the GMB union, said: "When the pipes are laid, they have to be supported properly underneath, especially where they join. But it doesn't appear as if this happened and the pipes have dropped, causing them to become buckled.

"Apparently they are now going to have to dig up the pipes and repair them but that is a process that is going to take months. It's just one disaster after another."

On Monday engineers said a rafter on the north roof collapsed without warning, falling about one metre, as several men were working on it. The section of the roof where the incident happened was being investigated to find out what caused the 50-tonne steel rafter to move.

The incident followed an announcement last month that the stadium would not be ready for the May 13th FA Cup final, as originally planned, and the game would instead be played at the Millennium Stadium in Cardiff.

England's two World Cup warm-up friendly matches - against Hungary on May 30th and Jamaica on June 3rd - will now be played at Old Trafford. The FA had already allowed Multiplex to move the completion deadline several times.

The original autumn 2005 handover date was pushed back to January 31st 2006 and then March 31st.

The stadium was dogged by delays and problems even before the site was sold to the FA in 1998. The original £325million cost has more than doubled and there were numerous wrangles and problems in raising the money before construction got under way.