Hi Colin,
I wrote about how I done this a couple of years ago for The Courier using a kit from Maplins, but if you CLICK HERE you can find the same article.
The Club Shop sell the Smart-Screen kits which seem good, but a little pricey. Couldn't find them on the online shop, but they were advertised in the Mag that's just arrived or go direct to the manufacturer here: http://www.smart-screen.co.uk/contents/en-uk/d13.html
I have overcome the problem I initially posted, I am using the delay relay to switch a standard 4 pin relay as these can be switched as positive or negative, seems to work fine.