Immediately wash out your eye with plenty of fresh water under the tap, particularly where you have any irritant substances (i.e. bleach, acid or cement) in your eye. Keep going for at least 20 minutes.
Ask your GP for an urgent appointment or telephone advice, or call Out of hours call 111 if minor. But if you have a foreign body which is stuck or have been in contact with irritant substances go to Eye Casualty, King Edwards VII hospital, St Leonards Road, Windsor between 9 and 5.