Separation assembly for the flow measurement of a gas flow and a liquid flow of a multiphase fluid wherein the separation assembly comprises a) a separator with a housing and a separation element inside the housing, wherein the separation element is formed such that it provides the fluid to rotate by flow velocity, wherein the housing further comprises an inlet for a multiphase mixture and two outlets (22, 23), one primarily for pre-separated gas with some remaining liquid and the second primarily for pre-separated liquid with some remaining gas; wherein these outlets (11, 12) lead to a regulator b) wherein said regulator is part of the separation assembly and comprises at least two outlets (45, 46), one for liquid free gas and one for gas free liquid, wherein said regulator is provided to ensure the final separation of gas and liquid phases over an entire flow rate range to provide monophase liquid and gas at the outlets (45, 46) of said regulator, wherein the separation assembly is provided with a flowmeter for measuring the gas flow at the gas outlet of the regulator, and wherein the separation assembly is provided with a flowmeter for measuring the liquid flow at the liquid outlet of the regulator wherein the separation element is stationary with respect to the housing, characterized in that the separation element is an Archimedes type screw, wherein the form of the separation element provides a rotation to the incoming multiphase fluid so that the different densities of oil and gas forces the gas and liquid to separate due to the helical pathway of the screw and wherein the regulator comprises a housing in the form of a pipe, wherein the housing is provided with a liquid outlet and a gas outlet, and, in order to regulate the separation to achieve a monophase liquid and gas flow, the regulator is further provided with at least one float to regulate the gas and/or liquid outlet (45, 46) of the regulator. a) a separator with a housing and a separation element inside the housing, wherein the separation element is formed such that it provides the fluid to rotate by flow velocity, wherein the housing further comprises an inlet for a multiphase mixture and two outlets (22, 23), one primarily for pre-separated gas with some remaining liquid and the second primarily for pre-separated liquid with some remaining gas; wherein these outlets (11, 12) lead to a regulator a housing and a separation element inside the housing, wherein the separation element is formed such that it provides the fluid to rotate by flow velocity, wherein the housing further comprises an inlet for a multiphase mixture and two outlets (22, 23), one primarily for pre-separated gas with some remaining liquid and the second primarily for pre-separated liquid with some remaining gas; wherein these outlets (11, 12) lead to a regulator b) wherein said regulator is part of the separation assembly and comprises at least two outlets (45, 46), one for liquid free gas and one for gas free liquid, wherein said regulator is provided to ensure the final separation of gas and liquid phases over an entire flow rate range to provide monophase liquid and gas at the outlets (45, 46) of said regulator, wherein the separation assembly is provided with a flowmeter for measuring the gas flow at the gas outlet of the regulator, and wherein the separation assembly is provided with a flowmeter for measuring the liquid flow at the liquid outlet of the regulator wherein the separation element is stationary with respect to the housing, characterized in that the separation element is an Archimedes type screw, wherein the form of the separation element provides a rotation to the incoming multiphase fluid so that the different densities of oil and gas forces the gas and liquid to separate due to the helical pathway of the screw and wherein the regulator comprises a housing in the form of a pipe, wherein the housing is provided with a liquid outlet and a gas outlet, and, in order to regulate the separation to achieve a monophase liquid and gas flow, the regulator is further provided with at least one float to regulate the gas and/or liquid outlet (45, 46) of the regulator. wherein the separation assembly is provided with a flowmeter for measuring the gas flow at the gas outlet of the regulator, and wherein the separation assembly is provided with a flowmeter for measuring the liquid flow at the liquid outlet of the regulator wherein the separation element is stationary with respect to the housing, characterized in that the separation element is an Archimedes type screw, wherein the form of the separation element provides a rotation to the incoming multiphase fluid so that the different densities of oil and gas forces the gas and liquid to separate due to the helical pathway of the screw and wherein the regulator comprises a housing in the form of a pipe, wherein the housing is provided with a liquid outlet and a gas outlet, and, in order to regulate the separation to achieve a monophase liquid and gas flow, the regulator is further provided with at least one float to regulate the gas and/or liquid outlet (45, 46) of the regulator.