I would also speculate the arrest was made promptly after the tip off Rosie51- to manage the potential flight risk at earliest opportunity. All in order. Hoyle is not obliged to disclose the background of his information to the press. He was not obliged to say anything- but chose to do so, he said, to stop speculation specifically (against the MPS/CPS?).
PM and his legal team would know they can ask police for details of evidence, as they did, but also know the police are not obliged to make full disclosure at investigation phase. It was an intentional, quite aggressive, publicity oriented tactic. PM knows the media game well but this time was thwarted by Hoyle's public statement. Most likely, the intention was to get on the front foot v MPS/CPS on back foot in the public perception. If and when the case gets to court- the jury will be made up of members of the public and they probably will have read newspaper articles etc.
Whilst in investigation phase, as are both AMW and PM (pre charge) allows the defence to ask questions, understand the evidence and potentially raise issues to prevent charges being brought- but the police are not obliged to make full disclosure of their case file. They will reveal (just) enough evidence to allow for a proper response in interviews.