(33)To preserve the effectiveness of official controls in the verification of compliance, no notice should be given prior to performing controls, unless such prior notice is absolutely necessary for the controls to be carried out (for example, in the case of those official controls performed in slaughterhouses during slaughter operations which require the continuous or regular presence of staff or representatives of the competent authorities in the operator’s premises) or the nature of the official control activities requires otherwise (as is particularly the case with regard to audit activities).