Cristiano Ronaldo has turned from the accused into the accuser by criticising the standard of refereeing in England and complaining that he is not afforded enough protection.

Ronaldo rejected allegations that he was a diver and the Manchester United winger appealed for Premiership officials to take a tougher stance against the "dirty" opponents he claims are trying to kick him out of the game.

"The referees favour the defenders," said Ronaldo. "For some reason referees think I should be able to protect myself without their help. If it's a free-kick, the referee should give a free-kick. But here referees choose to ignore fouls a lot of the time. The football's different here, with a different mentality, and it's not just the players who have grown up with it but the referees, too. I just want to play football but sometimes I get angry about it.

"It's difficult for a defender in England to get sent off by collecting two yellow cards. It's very rare that happens. But the referees should protect the attackers more - not only me, not only wingers, but strikers as well. If it's a dirty tackle or a harsh tackle, the referees should give a yellow card right away without warning. But they don't. Instead the defenders are often told: 'Next time it's a booking'."

Quoted in Manchester United's new Opus publication, Ronaldo was speaking, in Alex Ferguson's words, as "the most fouled player in the Premiership" and, although that is statistically not true, United believe they are entitled to complain about the treatment the Portuguese international receives from opponents.

Ferguson was infuriated, for instance, that Manchester City's Joey Barton was not booked for a scything challenge on Ronaldo in the first minute of Saturday's derby game at Old Trafford. "I've had some bad tackles on me," said Ronaldo, "but I always get up whereas other players will roll around. So the referees think there's nothing wrong with me."

Critics may think that rich coming from a player who has one of the worst reputations for trying to dupe referees and was accused of cheating by the Middlesbrough manager, Gareth Southgate, earlier this month. Yet Ronaldo said he had nothing to be ashamed of and insisted that diving was no longer part of his repertoire. "In the first year I was with United I was criticised quite a lot for going to the floor too easily," he said. "That was an area of my game where I had to change quite fast."

All the more so since video replays could soon be used to punish players guilty of diving if the Football Association succeeds in convincing Fifa it is in the best interests of the game. The FA hopes to raise the issue of retrospective punishments when the International Football Association Board convenes in Manchester in March.

Meanwhile, 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.