Along with the steamer, you'll need a wall paper perforator, seen here:
http://www.zinsser.com/product_detail.asp?Prod uctID=20 .
The steamer is a good idea, but it can be messy. I've had really good luck with products like this:
http://www.wallwik.com/products/wallwik-power- solution.html .
Of course, these are products available here in the U.S., but I'm sure something similar can be found in the U.K. at most DIY stores.
It's easily applied with either a paint roller or my favorite a common garden sprayer. The warmer the water, the better. It's especially good in removing the remaining paste from the walls...
Good luck!