I recently watched a BBC series called "Life on Mars". It's mainly about policework in the 70s, and a more or less typical crime series. In this series, however, the few times a lawyer was present at a suspect's interrogation, the lawyer, when confronted with the fact, that the police wished to keep the suspect in their cells a bit longer, so he could be interrogated some more, and so that he wouldn't flee, the lawyer would always say something like "that's not my client's problem", and simply walk away, together with his client.
So now I'm wondering, if there is no legal figure of any kind in Britain that would allow the police (or prosecution, or whoever leads investigations after charges have been pressed) to keep important suspects under custody (in order to prevent them escaping, or influencing witnesses, or the like), or if the conditions under which such a figure might be executed are so hard to meet (or if the writers just didn't consider it).