The message
from "Pam Morris" contains these words:

Can anyone suggest/recommend horizonal growing plants - preferably
evergreen, low maintenance & fast(ish) growing. The only one I can think of
is the prostrate cotoneaster and that's only because I already have one of
them! Planting position will be a south facing, slightly sloped gravel bed.

TIA.

There are some horizontal junipers such as Juniperus horizontalis
'Prince of Wales' or J. horizontalis 'Youngstown'. They're probably not
as fast growing as Cotoneaster but they're certainly low maintenance.
There are also different horizontal cotoneasters in addition to C.
horizontalis - for example, C. x suecicus 'Coral Beauty' - but that may
be the one you have already.
Janet G