A lengthy statement explains why officers arrested the Republic protesters ahead of the King’s coronation.
The force said it believed items found alongside a large number of placards could be used as “lock on devices”.
“The investigation team have now fully examined the items seized and reviewed the full circumstances of the arrest,” a statement added.
“Those arrested stated the items would be used to secure their placards, and the investigation has been unable to prove intent to use them to lock on and disrupt the event.
“This evening all six have had their bail cancelled and no further action will be taken. We regret that those six people arrested were unable to join the wider group of protesters in Trafalgar Square and elsewhere on the procession route.”
Graham Smith, chief executive of the anti-monarchy Republic campaign group – who was among those arrested on Saturday, tweeted: “We have just been told that the police will be taking no further action.
“This has been a disgraceful episode and we will be speaking to lawyers about taking legal action.
“I also expect a full inquiry into why they repeatedly lied to us and who authorised the arrests.”