Social media companies are "undermining" counter terrorism investigations by telling suspects when police have requested their communications data, the assistant commissioner of the Metropolitan Police has said.
Mark Rowley, the UK's most senior counter-terrorism police officer, said some companies simply refuse to assist the police when it comes to handing over data.
He warned that the police are dealing with a "growing number of blind spots" and that difficulties relating to obtaining communications data and encryption mean that "all counter terrorism operations are now more patchy in their intelligence than we have ever seen before".
"Our experience of social media and communications companies is of a very fragmented and highly variable level of cooperation, ranging from some who are very cooperative, those who are partially cooperative and those who are at the other end of the spectrum," he warned during a speech at the Royal United Services Institute.
"Some refuse to assist. For some it is also a part of their strategy - they design their products in full recognition that they will be unable to help us because of the way they have designed them.
"And some simply undermine us by adopting a policy that if they supply data to us they will tell the subject that they have done that."
Mr Rowley said social media is an "immature business sector" and that the way some companies behave would not be tolerated in other sectors.
He said: "In the real world, if someone was to open a shopping centre in London with a fantastic new business model which made them large amounts of profit but also provided a safe operating environment for criminals or terrorists we wouldn't allow it.
"Yet to some degree that is what is going on in the virtual world."
Meanwhile, criminals and terrorists are now "better educated" about where the police and intelligence agencies may have "blind spots".
"From a policing perspective, any area which is no-go to police and intelligence agencies because we don't have the powers or the technology or the ability to reach there is a space that terrorists and criminals can operate and is of massive concern," he said.
The assistant commissioner also detailed the scale of work currently being undertaken by the Met in the fight against terror.
He revealed police are dealing with about 600 referrals from across the country every month relating to specific concerns about individuals.
The UK's terror threat level is currently set at "severe" which means an attack is "highly likely" and Mr Rowley said six terror plots have been disrupted in the last years.
He also noted there has been a significant increase in the number of people being arrested on suspicion of terror offences in the UK - currently about 90 to 110 people every quarter.