Officers will begin questioning the four people - identified as arguidos, meaning formal suspects - tomorrow at a police station in Faro, Portugal.
Eight key witnesses will also be questioned.
The three-year-old vanished while holidaying with her parents in Praia da Luz in 2007.
in ITV News, 30 June 2014, 6:54pm, (unsigned)
A few things on the above ITV
1. Metropolitan Police can't question anyone, they can sit in on the interrogations just like PJ did in April 2008 in the UK.
2. From past leaks, of unknown provenance, it's likely that the 8 witnesses are 5 former Ocean Club workers and the 3 house burglars.
3. However it is also likely that the 4 alleged arguidos are part of that group, or maybe they are an entire set of different people of interest to the Metropolitan Police investigation.
4. If the unknown 4 were constituted as arguidos, the possibility is that that was done so they can refuse to reply, so they won't incriminate themselves, whilst as mere witnesses they would be forced to answer. Like Kate McCann, as arguida, refused to answer the 48 questions put to her in September 2007 by the Judiciary Police.
5. Legal disclaimer. I'm not a lawyer and what I just posted above, is my opinion, I could be wrong, and if I am feel free to correct me.
6. Can't help notice the coincidence of the timing, that will once again overlap with the McCanns versus Amaral trial.
Update at 20:45pm
11 people to be questioned as witnesses and 4 to be questioned as arguidos - PT media reports via TVI.
Sergey Malinka is one of the 4 arguidos to be questioned in the scope of the English rogatory request - PT media reports on SIC Notícias
Update July 1 2014, 13pm
One arguido is a former Ocean Club driver, the second a young man, the third a man with psychiatric problems & the fourth Malinka. The connections between them are alleged to be phone calls done in May 2007.
TVI 24, broadcast 30 June 2014
TVI News anchor - There are new developments in the Madeleine McCann case: At the request of the British authorities four people will be constituted as arguidos. The interrogations are going to take place tomorrow in the Judiciary Police headquarters in Faro, and they [the police interrogations] are going to be attended by the Scotland Yard detectives. There are at least 11 people who are also going to be questioned under a witness status. These steps were requested in the letters rogatory, and have solely to do with the British investigation.
Sic Notícias, broadcast 30 June 2014
Sic News journalist - The step was fulfilled by the PJ, confined to an English request made via letter rogatory: three Portuguese and one Russian are from this moment on formally arguidos, within the scope of the English investigation into the case of Maddie's disappearance. In the case of the Russian citizen, it is already the second time that his name appears connected to the case. In 2007, at the time of the initial Portuguese investigation he was also constituted as an arguido [sic, he was not constituted as arguido - R. Murat, K. and G. McCann were the only arguidos of the PJ 2007/08 investigation] and was target of house searches which came to nothing.
Nonetheless, the Metropolitan police, after reviewing the whole process, officially requested for Sergey Malinka to be questioned again as an arguido. There are three other suspects to the British investigation, residents in Praia da Luz, who, from this moment on, are also arguidos following the analyses of the mobile communications of phone calls done on the night the child disappeared. The fact that all of these men live near to one of the sites where the Scotland Yard believed that Madeleine could have been buried, was another one of the justifications used by England [sic] to substantiate their suspicions.
These four arguidos and about eight witnesses are going to be questioned by the Judiciary Police as soon as this Tuesday, in the presence of Scotland Yard officers. Between inquiries and interrogations, these proceedings are likely to be prologued until Friday. All these steps have exclusively to do with the English investigation, which has not found any echo on the investigative line of enquiry being followed by the Judiciary Police.
Related: Martin Brunt on Sky News reports: 'Madeleine McCann Police To Interview Suspects'
BBC - Madeleine McCann suspects to be questioned by police (unsigned)
Guardian - Madeleine McCann suspects face questioning as Met arrive in Portugal by Brendan de Beer
*legalese in a comment bellow will be translated tomorrow, sorry