Why not be brave, rip out all that nasty ivy with as much of the roots as you can (a hands and knees job), and replace with a couple of nice Montana clemetis that will cover the shed in no time. Initially you'll have to keep a close eye on the ivy trying to return, and the area will look a little bare, but once the Montana is everywhere it will all have been worth while!

Southfacing wall/fence in London - the world's your oyster, don't waste such an area by letting ivy grow there. Get the ivy out altogether, anything else you try planting there won't be able to compete with it. Easily said, I know, and much harder to do, but worth it - put trellis or mesh up and grow Tracheleospermum jasminoides, evergreen, fragrant white flowers in summer. Or Campsis grandiflora, fabulous exotic orange trumpet flowers in summer, but deciduous.

Thank you so much for your advice, We were hoping that there was going to be an easier solution than digging up the ivy, but we shall press ahead and take your suggestion. Tracheleospermum jasminoides seems an amazing plant and montana seems an obvious choice. I guess we can grow them together as the fence is large enough to accomodate both.

Regards

Roubina

Blimey, must be a hugely long fence then - montana gets 30 feet...