A filtration membrane which comprises a porous support and, covalently bonded to a surface thereof, a continuous layer comprising a plurality of vesicles having transmembrane proteins incorporated therein, said vesicles being formed from an amphiphilic block copolymer, and said transmembrane proteins being selected from aquaporins and glyceroporins; beta-barrel transmembrane proteins; and alpha-helical transmembrane proteins; characterised in that within said layer, vesicles are covalently linked together to form a coherent mass in which said layer of vesicles has a thickness greater than the average diameter of the vesicles, wherein said amphiphilic block copolymer is a diblock copolymer AB having a hydrophilic and a hydrophobic block or a triblock copolymer ABA having hydrophilic end blocks and a hydrophobic inner block, wherein the filtration membrane may be prepared by a process that comprises providing an aqueous suspension of vesicles having transmembrane proteins incorporated therein, said vesicles being formed from an amphiphilic block copolymer having reactive end groups; depositing said suspension of vesicles on a surface of a porous support; and providing reaction conditions such that covalent bonds are formed between different vesicles and between vesicles and said surface, wherein the process comprises: (i) (a) providing a first aqueous suspension of vesicles having transmembrane proteins incorporated therein, said vesicles being formed from amphiphilic block copolymers having reactive end groups X; (b) providing a second aqueous suspension of vesicles having transmembrane proteins incorporated therein, said vesicles being formed from amphiphilic block copolymers having reactive end groups Y which are reactive with polymer end groups X; (c) depositing said suspensions of vesicles on a support having a surface which is reactive with either polymer end groups X or Y; and (d) causing reaction of end groups X with end groups Y, and either end groups X or end groups Y with the surface of the support; or wherein the process comprises: (ii) (a) providing an aqueous suspension of vesicles having transmembrane proteins incorporated therein, said vesicles being formed from amphiphilic block copolymers having reactive end groups X; (b) providing an multifunctional linking agent having at least two reactive groups Y which are reactive with polymer end groups X; (c) depositing said suspension of vesicles and said multifunctional linker on a support having a surface which is reactive with either polymer end groups X or reactive groups Y; and (d) causing reaction of end groups X with groups Y, and either end groups X or groups Y with the surface of the support. and wherein in either (i) or (ii), groups X are amine groups and groups Y are carboxylic acid, activated carboxylic acid, and/or azide groups; or groups X are carboxylic acid, activated carboxylic acid, and/or azide groups, and groups Y are amine groups; or groups X and Y are click chemistry groups. (i) (a) providing a first aqueous suspension of vesicles having transmembrane proteins incorporated therein, said vesicles being formed from amphiphilic block copolymers having reactive end groups X; (b) providing a second aqueous suspension of vesicles having transmembrane proteins incorporated therein, said vesicles being formed from amphiphilic block copolymers having reactive end groups Y which are reactive with polymer end groups X; (c) depositing said suspensions of vesicles on a support having a surface which is reactive with either polymer end groups X or Y; and (d) causing reaction of end groups X with end groups Y, and either end groups X or end groups Y with the surface of the support; or wherein the process comprises: (a) providing a first aqueous suspension of vesicles having transmembrane proteins incorporated therein, said vesicles being formed from amphiphilic block copolymers having reactive end groups X; (b) providing a second aqueous suspension of vesicles having transmembrane proteins incorporated therein, said vesicles being formed from amphiphilic block copolymers having reactive end groups Y which are reactive with polymer end groups X; (c) depositing said suspensions of vesicles on a support having a surface which is reactive with either polymer end groups X or Y; and (d) causing reaction of end groups X with end groups Y, and either end groups X or end groups Y with the surface of the support; (ii) (a) providing an aqueous suspension of vesicles having transmembrane proteins incorporated therein, said vesicles being formed from amphiphilic block copolymers having reactive end groups X; (b) providing an multifunctional linking agent having at least two reactive groups Y which are reactive with polymer end groups X; (c) depositing said suspension of vesicles and said multifunctional linker on a support having a surface which is reactive with either polymer end groups X or reactive groups Y; and (d) causing reaction of end groups X with groups Y, and either end groups X or groups Y with the surface of the support. (a) providing an aqueous suspension of vesicles having transmembrane proteins incorporated therein, said vesicles being formed from amphiphilic block copolymers having reactive end groups X; (b) providing an multifunctional linking agent having at least two reactive groups Y which are reactive with polymer end groups X; (c) depositing said suspension of vesicles and said multifunctional linker on a support having a surface which is reactive with either polymer end groups X or reactive groups Y; and (d) causing reaction of end groups X with groups Y, and either end groups X or groups Y with the surface of the support.