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Formula 1 bosses have changed the rules to prevent drivers 'blocking' a rival who is trying to pass them.

The move was prompted by an in Italy last season.

The new rule, officially published on Wednesday, forbids drivers from moving back on to the racing line if they have moved off it to defend.

It formally enshrines what had previously been an agreement between the drivers.

The new rule is .

It says: "More than one change of direction to defend a position is not permitted.

"Any driver moving back towards the racing line, having earlier defended his position off‐line, should leave at least one car width between his own car and the edge of the track on the approach to the corner."

It is this that so incensed Hamilton about Schumacher's driving in Monza - there was one incident between the second chicane and the first Lesmo corner which prompted the Englishman to get on the radio to his team and say: "I thought you were only allowed to make one move."

Schumacher's Mercedes team received a number of warnings from race director Charlie Whiting during his defence in Italy, and team boss Ross Brawn went on the radio to remind him to "leave room" for Hamilton when he was defending.

The previous rule that forbids drivers from forcing rivals off the track remains.

It is article 20.3 and it reads: "Manoeuvres liable to hinder other drivers, such as deliberate crowding of a car beyond the edge of the track or any other abnormal change of direction, are not permitted."

The new sporting regulations also forbid drivers from "leaving the track without justifiable reason", an attempt to stop them taking shortcuts back to the pits during practice and qualifying to save time and fuel - as Sebastian Vettel did in Korea.

And in article 40.12, they lay out circumstances under which lapped cars can unlap themselves during a safety car period.

The epic 2011 Canadian Grand Prix, which ran for four hours and four minutes following a two-hour mid-race stoppage for torrential rain, has led to a new rule restricting the maximum length of races, including stoppages, to four hours.

And the penalties against which teams are not able to appeal have been laid out in the rules.

These are any drive-through or time penalty imposed for a driving infringement during the race, a driver being excluded from the race on the grounds he did not set a time within 107% of the fastest in the first qualifying session; and not having all the wheels on the car three minutes before the race.