Sir Bernard Hogan-Howe has said government cuts to the police budget could risk public safety.
The Metropolitan Police Service commissioner believes Britain faces years of austerity regardless of who was in Number 10 and recommended forces across England and Wales pool resources with other emergency services.
Writing in the Guardian, Hogan-Howe highlighted how the Met would have slashed £1.4bn from its budget by 2020 but said the force would be cutting close to the bone from 2016.
The commissioner said unless forces shared resources, "public safety will suffer".
"We have to have a shared view of the risks to public safety, from countering terrorism to child protection," he wrote.
"We must be open about these risks with the public, politicians and the media, so we can together make informed choices about our priorities. We should share support services where possible, and make them as efficient as the best of the private sector."
He called for "radical action" in the face of outdated county boundaries that sees 43 police forces operate across England and Wales.
Advocating a merge of emergency services, Hogan-Howe said: "Bring them together and it would be cheaper to run and more effective.
"With each blue light service responsible to a different ministry, there are obstacles to change. Will the next government be brave enough to bring together public safety services? Yes, it is a risk. But there's a bigger risk to public safety if we don't take radical action."