The red key you have in your inventory needs to be used on a red 'dry riser' box located at the entrance to Alfie's home (no cursor help on the box I'm afraid). The same key will be used on a similar box in the next location!
I'm wondering if I've made this game a tad too difficult (though lots of people have completed it).
I'm in the process of creating a hints list and maybe even a walkthrough to put on my website. The hints will be based on user feedback.
In the meantime ... feel free to post comments, queries etc ... I will do my best to help