I have no idea on what the average payout is and each case will depend on individual circumstances. I keep being told its around £2-3K, but that's from ambulance chasers.
However, you could try the websites of the financial trade bodies to see if they give you any help, e.g. what is taken into account; formula used etc. I would suggest you look at the British Bankers Association; the insurance equivalent (ABI); FSA and Financial Ombusman. Also look at individual banks websites in case they have anything.
Sorry can not be more helpful