A process for the conversion of a hydrocarbon feed with a sulphur content of at least 0.1% by weight, an initial boiling point of at least 300°C and an end point of at least 440°C, in which: a) said feed undergoes a hydrodemetallization treatment in a fixed bed hydrodemetallization section comprising one or more fixed bed hydrodemetallization zones preceded by at least two hydrodemetallization guard zones, also fixed bed, disposed in series for use in a cyclic manner consisting of the successive repetition of steps a") and a"') defined below: a') a step in which the guard zones are used together for a period at most equal to the deactivation and/or plugging time of one of them; a") a step during which the deactivated and/or plugged guard zone is shortcircuited and the catalyst it contains is regenerated and/or replaced by fresh catalyst, and during which the other guard zone(s) is/are in use; and a"') a step during which the guard zones are used together, the guard zone for which the catalyst has been regenerated during the preceding step being reconnected and said step being continued for a period at most equal to the deactivation and/or plugging time of one of the guard zones; b) at least a portion of the at least partially demetallized effluent is hydrocracked in a hydrocracking section containing at least one fixed bed hydrocracking catalyst; c) at least a portion of the at least partially hydrocracked effluent undergoes fractionation in order to obtain a light fraction and a heavy fraction; d) at least a portion of said heavy fraction is hydrodesulphurized in a hydrodesulphurization section containing at least one fixed bed hydrodesulphurization catalyst, and into which hydrogen is reinjected. a) said feed undergoes a hydrodemetallization treatment in a fixed bed hydrodemetallization section comprising one or more fixed bed hydrodemetallization zones preceded by at least two hydrodemetallization guard zones, also fixed bed, disposed in series for use in a cyclic manner consisting of the successive repetition of steps a") and a"') defined below: a') a step in which the guard zones are used together for a period at most equal to the deactivation and/or plugging time of one of them; a") a step during which the deactivated and/or plugged guard zone is shortcircuited and the catalyst it contains is regenerated and/or replaced by fresh catalyst, and during which the other guard zone(s) is/are in use; and a"') a step during which the guard zones are used together, the guard zone for which the catalyst has been regenerated during the preceding step being reconnected and said step being continued for a period at most equal to the deactivation and/or plugging time of one of the guard zones; a') a step in which the guard zones are used together for a period at most equal to the deactivation and/or plugging time of one of them; a") a step during which the deactivated and/or plugged guard zone is shortcircuited and the catalyst it contains is regenerated and/or replaced by fresh catalyst, and during which the other guard zone(s) is/are in use; and a"') a step during which the guard zones are used together, the guard zone for which the catalyst has been regenerated during the preceding step being reconnected and said step being continued for a period at most equal to the deactivation and/or plugging time of one of the guard zones; b) at least a portion of the at least partially demetallized effluent is hydrocracked in a hydrocracking section containing at least one fixed bed hydrocracking catalyst; c) at least a portion of the at least partially hydrocracked effluent undergoes fractionation in order to obtain a light fraction and a heavy fraction; d) at least a portion of said heavy fraction is hydrodesulphurized in a hydrodesulphurization section containing at least one fixed bed hydrodesulphurization catalyst, and into which hydrogen is reinjected.