SILVERSTONE, England - Red Bull was caught off-guard when driver Mark Webber announced he was leaving leaving Formula 1.Team boss Christian Horner said Webber phoned him before the statement from Porsche was issued.Horner said: "I had a call this morning and that was the first I knew about it. He's obviously decided to take things into his own hands. I think probably the guys in the factory are a bit disappointed that they read it on the internet rather than heard something direct."That's the way these things are sometimes... I suppose an hour's notice is a bit short." Team mate and triple World champion Sebastian Vettel found out much later.'DECISION A GOOD ONE'Webber said: "It was a Porsche announcement. I informed Christian before the announcement, which contractually I should do, so that's what we did. I will talk to the factory at some stage. They've been superb for me but Porsche was very keen to make the announcement. It was about Porsche and Mark Webber today."Red Bull owner Dietrich Mateschitz said he had known about Webber's plans for some time. "We knew about Mark's decision and I think it's a very good one with benefits for him and Porsche." Speculation linking Webber to Porsche first surfaced earlier in 2013, with the veteran driver denying claims he was set to quit F1. Webber said: "The decision has been there for quite a long time actually. I've known for quite a while, I've had a plan and I've stuck to it. Dietrich has been completely up to speed with my thinking in the last six to eight months."F1 RULE CHANGES BLAMED?Webber said the rule changes for 2014, when a new V6 engine will be introduced,played a part in his decision but he had also been complaining for much of this season about the current situation with tyres that do not allow him to race flat-out."There's lots of reasons that come into the pot when any sportsman or woman wants to call it a day. There's going to be big, big changes in this sport in 2013 so I may as well go and do those big, big changes where my future is going to be."Webber said he would be fully motivated and committed right to the end of the season in Brazil and Horner expected no less from him.Ferrari's Fernando Alonso said: "I think he'll have a lot of fun, as he's doing now, with a little bit less problems than we have now in F1. I wish him the best of luck for the rest of the championship and for future."