Yes trains do use that, but there is no regular service from Amersham to
Watford, although they may have to use that route in an emergency.

Nigel wrote:

Can anyone please tell me - Is the Watford Curve ever used from the
Rickmansworth end, this is the curve with the short tunnel, are trains
ever run from Amersham to Watford, or vive versa?

Nigel