It is claimed that three police forces, including the Met Police, may not be able to function properly because of government cuts. HM Inspecorate of Constabulary says around 6,000 officers will be axed from the frontline in England and Wales.
Spending on goods and services will also be cut by about £474 million.
At least 179 police stations will also have closed by 2015, and 264 stations will have lost their front counter, HMIC said.
Sir Denis added that police stations, even those which offered no public access, were often seen as a reassuring sign of control in communities.
These will be replaced by 137 police access points in "shared locations", such as supermarkets, it said.
The memorial service will be attended by Prince Harry and Meghan Markle.
David Browning admits manslaughter by diminished responsibility but denies murder.
Four people have died and the suspect is still at large, police said.