I am not sure why police numbers are an issue. In all three of the latest terrorist events they have performed commendably - particularly in the latest.
If there has been a failure it is in the security services who, it appears, had plenty of information on at least one of the latest 3 killers; and the budget for the security services has been massively increased over the last 10 years - including funding for another 2000 members in 2015.