Commission, I wouldn't know exactly but I'm guessing it would vary depending on how much individual input you had, how important/valuable the deal is etc etc. But, from what I can understand, on average you'd probably be looking at 1.5-2% of the value of each deal.
Say, for example a sale is worth £8,000 in interest to the company per year. You may recieve commission as a percentage of that each year, or as lump sum relative to the total worth of interest over a fixed period. Say, it's worth £40,000 to the company over five years, you may recieve a percentage of that as a lump sum at the end of the year.
Sorry, that seems pretty confusing but I hope you get my drift.