Why?
The police say its security operation is "sucking" their resources. The easy solation to that is to cancel it, it is not necessary. If, and it is a big "if", security is needed it is up to the Ecuadorian Embassy to provide it.
Assange sought refuge in the Ecuadorian Embassy in order not to be extradited to the USA via Sweden. He wandered in, asked for asylum, and was allowed to stay. He is their problem.
The Met's "security" operation is not really security due to some maniacs trying to bump him off, though the CIA might be thinking of ways, it is all down to making sure that he is prevented from ever leaving the embassy. He has broken no UK laws, so their 24/7 surveillance is purely to keep him imprisoned on behalf of the Swedes and Americans. Let them pay.