I think it depends how much you go over. Mine went over this month (foolishly not working out exchange rates) by about £17 and nothing happened, when I realised I checked online and it was flashing red self-destruct signs at me (Barclaycard) but then just said, "oi, you need to get below your limit" so I transferred some that day, and on this month's statement there are no additional charges.
ok cool. its only £35 showing at the moment but my online banking doesn't update straight away so its only transactions up to 29th oct. im waiting for dp to get back to me with whatelse he has spent since then.
there is also £50 interest charges from last month and until i speak to the credit card people tomorrow i wont be able to see if the charges have been added yet or not
My impression is that it is possible to go over the limit if you are using the card for smaller purchases that don't require authorisation. I think the card will be declined if a large purchase is attempted that requires the vendor to verify/authorise with the credit card company.
I went over my Egg Card limit by about the same amount (maybe even less) - I too didn't even realise as DP sometimes puts things on the card too (I didn't even realise I had a limit!) I got a fine of £17 I think it was. I rang Egg as I needed to use the card abroad the next week and wanted to check I could and got a sarky woman on the other end who gave me loads of hassle and was so rude that I wrote them and complained. In the end I got my fine paid back into my account...althought they wouldn't uphold my complaint that the woman had been rude but as long as I got my money back that was all I cared about!
ive already rang HSBC and they said because ive gone over the limit i need to speak to the credit card management department and there is no one there until tomorrow so cant speak to them til tomorrow.
Basically they will say it is your responisbilty to keep within your limit and if you don't they will make a charge. I'm not sure so check but think it is one of the things recorded on your credit file now as well.