It has been discovered that Wembley's retractable roof will take 40 minutes longer to close than originally planned.

Initial plans stating that the roof would take 15 minutes to close have had to be changed because of safety concerns.

Engineering magazine New Civil Engineer has discovered that the process will now take 56 minutes and 30 seconds — and recommends that the roof is shut only when the stadium is empty.

But Wembley National Stadium Limited told the Guardian's official website, www.guardian.co.uk, the FA Cup final would not be affected by the discovery. A spokesman explained:

"This won't be a problem on FA Cup final day, because we will decide in the morning whether or not the roof will be open."

However, it is yet to be established whether changes in the roof-closing process may cause problems at other times.

The spokesman added: "We were aware of the change to moving times, and this formed part of our recent negotiations with Multiplex."

The development of the new Wembley stadium has not been smooth — although the Football Association, Wembley National Stadium Limited and builders Multiplex settled all their outstanding disputes regarding the construction of and payments for the facility last month.

It means the north London venue should be ready for next year's FA Cup final, which is due to be played on May 19.