The maximum fine for breach of condition notice (BCN) is £2,500. The recipient can be charged with subsequent offences if they continue to fail to comply. If charged with failing to comply with a BCN, it is up to you to prove that you had a reasonable excuse for non-compliance.
In the event of BCN non-compliance, or recurring breaches of the terms of the BCN, you will be asked to demonstrate what steps you have taken to comply with the conditions stated in the notice. If you cannot give a reasonable explanation or have taken no steps to comply, then your local council will likely seek to prosecute.
NEVER ignore a breach of condition notice.