Hi Damian,
How about this example.

create table data (
company_id integer,
key integer,
data integer
)

create table useraccess (
company_id integer,
user_id varchar(8))

create view u_data (key, data) as
select d.key, d.data from data d join useraccess u on u.compang_id
= d.company_id where u.user_id = current_user;

If you give all your users access to the views only then they can
only ever see the information for the company they can see. If you
want a user to be able to see multiple companies data, return the
company_id in the view and allow multiple companies per user in the
useraccess table.

Regards
Ian Newby