Each region in England and Wales has a special operations unit (SOU), working across county boundaries to tackle terrorism and serious organised crime.
The Eastern Region SOU, external includes more than 850 police officers and staff, covering Bedfordshire, Cambridgeshire, Essex, Hertfordshire, Kent, Norfolk, and Suffolk.
Forces in the East of England also share ideas and try to reduce duplication through the eastern region innovation network, external.
Northamptonshire is a member of the East Midlands SOU, while Thames Valley is part of the South East SOU.
Bedfordshire, Cambridgeshire and Hertfordshire forces also collaborate in several other areas.
They have shared major crime, roads policing, dog and scientific support units, as well as collaborating on armed police, firearms licensing and human resources.
Likewise, Norfolk and Suffolk have a special operations joint command, which includes criminal justice, roads policing, firearms, dogs, operational support and firearms licensing.
The two forces also share some IT and human resources functions.
According to Suffolk Police and Crime Panel, external papers for next week, the overall collaboration has saved the two forces a combined £57.6m.
Essex Police shares a serious crime directorate, external with Kent Police, which includes serious and organised crime, serious economic crime and modern slavery units.