They MIGHT (chances are not so high i suppose) send u a letter
as u areunable to pay your amount. U might get charged to court but
you won't get jailed, maybe just fined or something else. But if
you are unable to pay the fine, u'll go to jail instead.
You will also fall on their blacklist. Which means u have a record
of not paying bills, and they won't allow you to subscribe to their
service again. Furthermore, if you are the owner of your house and
holds a house telephone line, they will cut off your house
telephone line.
I suggest u try and pay them off ASAP.
Meanwhile, don't worry as they does give people a certain period of
time to pay off outstanding hp bills.