Why are you so keen to know? It's quite hard to be precise, and also depends on the firm.
Are you about to land a job as an IDB? Don't get worked up over the sums and what other people are earning. It's nice to have an idea, I admit, and that is probably that it is a few hundred thousand a year, around £350k I've heard , but it all depends on you making that money, not what other people have made.
If you need to find the entry rate to ensure you are being offered a fair deal then I reckon £35K+ for the first year if you are new to the game is a fair representation.
If I unearth anymore details from my friend i will tell you.