Most banks will give you a 24hr (or so) window before they issue a penalty and notify Equifax/Experian.
If you've never seen a credit report then the entry for your credit card (or whatever it is) would look a little like:
MadeUp Bank - Credit Card.
Limit £1,000,000
Balance £0.50
Previous Payment date & amount
Other dates
[Your details]
Payment History: 0 0 0 0 1 0
Where 1 would represent that you missed 1 months payment, or you were 1 month in arrears. It would change to 2,3,4 etc for more missed months (I think) up until D I think.
After the 6 months, that missed payment *should* disappear. Although my memory is fading, it could be 9 or 12 months they keep payment records of.
I don't think it would have much of an adverse affect on your rating if the rest of your record is intact.