The FA Cup semi-final between Manchester United and Manchester City has been described as ""a complete nightmare"" by police.

The bitter local rivals will face each other at Wembley over the weekend of April 16/17 in a match that is expected to be the most expensive security operation ever for a single football match, costing ""millions of pounds"", according to one source.
All FA Cup semi-finals have been played at the new national stadium in London since 2008.
Previously, all but a few semi-finals had been played at neutral club venues, but the FA now stages all semis at Wembley to help recoup the cost of rebuilding the stadium.
Should City qualify for the last eight of the Europa League, then the derby game would be moved to Sunday April 17, the same day as both Liverpool's Premier League clash at Arsenal and the London Marathon.
With the majority of fans travelling to the 90,000-capacity venue from Manchester, the fixture will require a major joint-operation between Scotland Yard, Greater Manchester Police and British Transport Police, the latter force needed to keep fans separate on trains down to London.
A Scotland Yard source told the Daily Mail: ""From a security point of view, this is a complete nightmare. It will cost millions of pounds.""
(Source: Eurosport)