The filter unit is curved downward so once the cap has been unscrewed, the filter basket is removed by withdrawing the cap back and downward. If it will not withdraw, it is possible that a foreign body such as a hairgrip or pen cap has become lodged across the basket and digging into the filter housing. In which case the only solution is to wriggle the basket gently until the debris in the basket loosens and enebles the obstruction to collapse.
Swuz
March 2008