Hi Sue, if the arm is metal u can try to bend it down,but if this prob has happened recently it suggests that the rubber seal is damaged & continues to let in water regardless of the position of the ballcock (float),so i reckon a new seal kit is needed. The entire internals can be had from B&Q for about £10 so it may be better to replace the lot if yours is old,they are simple to fit & replace the old type easily.
David
July 2008