It could be a Mistral, I suspect early 80s (as it doesn't have a rivetted on headbadge, and it has the later transfer & font style), difficult without frame number to determine exactly the date.
General comment - components don't often help as they could be earlier or later, looks like it has some Campag Nuovo Record (rear mech and chainset anyway) though.
Very good bike...I have a Mistral (1978), but can date it exactly as I've had it from new!
Do some research on nkilgariff.com, best place for all things Holdsworth.
Co-founder of a V-CC section, member South Eastern Road Club and owner of - 2005 Bianchi Reparto Corse (modern), 1985 Raleigh SBDU Pro Super, 1984 Raleigh LU Corsa, 1980 Allin Stan Butler Special, 1978 Ron Cooper, 2 x 1970s Roberts, 1975 Bill Philbrook tourer, 1966 Raleigh Superbe Roadster 1964 Allin Stan Butler Special Belgique, 1951 Hobbs of Barbican S/C, 1950 Hobbs of Barbican S/C, 1947 Hetchins Super Special, 1908 Centaur Featherweight.