If it's a council one then pay it ASAP or it will escalate, usually there is a discount if you pay quickly. It will not go away and will get bigger and bigger and a bailiff will come and demand several hundreds of pounds. You can pay it now without prejudice and then seek to recover it if you think there is an avenue for that. If it's a private one then you can ignore, they usually send you threatening letters for a year or so, they rarely take you to court but they can.