Hi there,
I think the charge will be about �12.00 as long as you get it back within the limit pronto. As this is a one off it should have no impact on your credit rating.
It's wierd about them taking action regarding a �10 excess. In my experience this wouldn,t be a problem unless the debt remained outstanding for more than 35 days.
As a general rule, HSBC do not place information with Credit Reference Agencies unless things get really bad - i.e. formal demand - so this really should have no impact on your mortgage prospects.
Good luck!