Not that it's so relevant now, but we always have 24 hours in which to question a suspect, subject to their detention being required for that period.
After 24 hours, permission must be sought from a Superintendent to extend detention for up to 36 hours. This must also be justified and necessary.
After 36 hours, we go to a magistrate. These are more unusual for regular crimes, but not so uncommon in murder investigations. The magistrate can order detention without charge for a further 36 hours. Again, we must justify why a suspect cannot be released on bail, and show what the state of the investigation is, and what lines of enquiry are being pursued.
Finally, a warrant of detention can be further extended up to a maximum of 96 hours (for a total of four days in custody) by a magistrate, with all the same provisos as before. These are more unusual, but still not rare in murder cases. At the end of 96 hours, a suspect must be released - except in terrorism cases, which aren't relevant to discuss here.
The media has been reporting these routine procedures as sensational new developments in the case. I am, as you may know, a serving detective within the Metropolitan Police. I wholly assure you, they are nothing sensational and, despite the ridiculous media coverage - turning a real-life murder investigation into a circus - Avon & Somerset are going through absolutely normal processes. I have had to tune out of the press coverage, because I find it absolutely sickening.