Hi Crowf. Not sure what the surface area is but will check it out for you tomorrow. if possible. It's a 3 bed semi, by the way.
According to this website, insulating a cavity wall isn't a great idea......... [broken link removed]
Pumping in something like ecobead would probably be a much better option, and certainly much, much cheaper. I know a few people who've had it done and they're delighted with it. Thousands of tiny balls of stuff like aeroboard are mixed with a watery glue and pumped in through holes bored in the wall. Simple enough job. And a grant of up to €400 is available for it..... [broken link removed]