Thanks scrambler. What I have done to get to where I am is pretty convoluted but I will try set it up on my test site and see if it works. I think the complication comes in because I have used a 2 column split, moved the left column content over to one side and put a background image so that it looks like it is the other half of the page. But now making the column and/or content stretch is a pain in the ass!
The content area height is currently just set by the text that is in it. so I can stick a load of spaces to make it reach the bottom, but then of course on a different browser you have a lot of dead space (although just thinking now I could use the “hide if mobile shortcode”).
Thanks for your time mate.