Ben Foster has completed his £6m move to Birmingham, with Sir Alex Ferguson insisting the former United goalkeeper will be England's future No1. The 27-year-old leaves Old Trafford having failed to establish himself as Edwin van der Sar's long-term successor, as well as missing out on Fabio Capello's World Cup squad. Ironically he replaces Joe Hart, who forced his way into Capello's plans after an impressive season on loan at St Andrews. But Ferguson, who only 12 months ago described Foster as the future for club and country, remains convinced the former Stoke keeper is the best in England. We accepted the bid from Birmingham City simply because we knew how concerned Ben was about his future and I can understand that, said the United manager. I think most of that comes from his disappointment of not having played enough games to get in the England squad this summer. I still feel very strongly about this, that Ben's the best England goalkeeper and I can't work out why he wasn't even considered simply because he didn't have enough football. Sometimes your conscience does come into it and you have to understand a player's feelings about it. Ben's been a terrific servant for us, he's been very unlucky with a couple of injuries he's had with us last season and I think he deserves the opportunity to do better for himself. Foster was expected to establish himself as United's No1 last season when a hand injury forced Van der Sar to miss the start of the campaign. Target But a series of blunders saw him slip down to third in the reckoning at Old Trafford, behind Tomasz Kuszczak. With Ferguson targeting a host of Europe's top keepers, including Hugo Lloris, Manuel Neuer, Igor Akinfeev and Sebastien Frey, it became clear that Foster's days were numbered. That opened the door for Birmingham manager, Alex McLeish, to make his move to replace Hart, who will return to City next season. Foster made just nine Premier League starts - his last appearance coming on February 23 against West Ham. Ferguson is expected to sign a top keeper this summer to replace Van der Sar, who will be 40 by the end of next season. But he revealed that England U21 international, Ben Amos, will be promoted to the first team squad. When we decided to let Ben Foster go, we were in the process of letting a good young goalkeeper, Ben Amos, go out on loan, he said. He's in the England Under-21 team but we can only accommodate three goalkeepers. So when the situation with Ben Foster's future at Manchester United came into it and we agreed to let him go, we stopped Ben Amos from going on loan. He will now be our third goalkeeper, he's very talented and has a good future ahead of him. So we have three goalkeepers, Edwin van der Sar, Tomasz Kuszczak and Ben Amos. So we're okay.