Hollies have male and female flowers on separate plants. To ensure berries therefore you will need a male and female plant. Some hollies will set fruit in the absence of a male but the resulting berries will have sterile seeds. The native UK holly is Ilex aquifolium.
Although hollies are usually pollinated by bees, their flowers lack nectary disks; sometimes the petals themselves produce nectar through swellings on their upper surface.(Enclyclopaedia Britannica)