Who should approve the maintenance program of an aircraft registered in a country other than Spain?

According to paragraph 3 of point M.1 of Annex I (Part-M) to Regulation 1321/2014: 

• the authority designated by the Member State of registration of the aircraft, or
• if, prior to the approval of the aircraft maintenance programme, the Member State of registry agrees, one of the following:
  • a)the authority designated by the Member State where the operator has its head office or, where the operator does not have a head office, the authority designated by the Member State where the operator has its place of establishment or residence;
  • b)the authority responsible for the oversight of the organisation in charge of managing the continuing airworthiness of the aircraft or with which the owner has concluded a limited contract in accordance with point M.A.201, letter i), punto 3.