If you ignore it & don't pay & don't come to (& keep) an instalment payment agreement then ultimately you could go to prison. But this sanction is very rarely used. If you are working it is much more likely that - after they have got the Court Liability Order - the Council (or bailiffs appointed by them) will get an attachment of earnings order to have the money deducted from your pay. There is a law setting out the % of your pay they can take. This % varies with the amount you are paid but it is really high so you would be well advised to come to some agreement straight away - but it must be for an amount you are willing & able to keep on paying & it must clear the arrears in a reasonable time as well as you paying the current bill.
If you need help with this get debt advice - go to your local CAB or ring CCCS.