Three flats share a small communal area where there are electrical meters and water piping cocks. Is there now a requirement for some kind of compartments within the cupboard? 

There always was to some extent, it's only in recent years it's been an area looked at to any degree. As there has to be a fire risk assessment for the premises this should detail the level of protection required - it could be a simple upgrade of the existing cupboard, new separation, protective enclosure over the meters, or even accepting the current set up (e.g. if all the electrical boards are in non combustible housings as per the most recent revisions of electrical installation regs)