this sort of activity is quite common, they call it harvesting.
they go after people who look like they have a good credit rating, they won't know for sure until you have applied, at that point they can do a full on credit search and establish your potential worth to them
motmann: the banks and financial institutions cannot, as far as i am aware, share/sell in depth information, they can pass it to other companies within the same group but for example HSBC would not be able to tell Lloyds what you have in your current account without your permission.
If you miss a payment on a load/credit card or any other financial commitment then they can report that to either experian or equifax, this is common business practice and is allowed, on the same token if you pay on time they will also share that info, so it can work for you as well as against you.
Egg have been planning this 'cull' of customers cards for a long time, they are not cancelling the accounts, they are taking the cards from customers for one reason or another, in light of the current financial issues in the US and UK i can see this being the first of many companies to do this, i believe Citicard are considering it as well.