Wrong. Sadly, unarmed bobbies were there within 5-7 minutes...but they did not approach the two (2) mooselimbs because there were weapons involved. You can see in the videos the bobbies at both ends of the streets creating a cordon.
However, you are correct in the fact that it took twenty (20) minutes for ARMED bobbies to arrive. They had to run to the barracks, sign out their MP5s and then rush to the scene. It was a miracle that they muzzies didnt get on that bus and stab everyone on it.