Wondering how much debt the average person is in.. Including mortgage, loans, credit cards, overdraft
If you want to find out about the average person's debt, you need to ask average people, which as you will have found, are in short supply on Mumsnet. 
.
When you say you owe money on credit cards, do you mean you use them for day to day expenses and pay off the balance each month, or you're paying interest on them? If that's the case it makes no sense
The person who has credit card debt, but far larger savings is probably someone who borrows at 0% and then saves the money at a higher rate. It's far less lucrative than it used to be, but you can borrow thousands of pounds at 0% and no fee for a year or two (and sometimes they throw in freebies like Amazon vouchers or other cashlike rewards on top).
You then put the money in an interest paying account until the end of the 0% period, and the profit is yours. I used to make hundreds of pounds a year doing this, others far more.