The label is missing, but with some research this appears to be a 1970s garden party dress from Bullock's and Wiltshire. They often featured romantic revival pieces that are highly sought after today:
Many of their 70s gowns were designed as a tribute to 1930s glamour, a trend sparked by the 1974 film The Great Gatsby. 
The design includes a square neckline, fluttering short sleeves, and a defined waistband that flows into a long, pleated A-line skirt. 
Hidden back metal zipper and exposed inside seams.
Sheer Overlays: It was common in the 1970s to see lightweight, sheer outer layers over a solid lining, creating a soft, dreamy silhouette.
Flutter & Angel Sleeves: These wide, loose-fitting sleeves were a staple of the era's "Boho" and "Peasant" trends.
Floral Motifs: Whether printed or embroidered, bold yet muted floral patterns in pinks and greens were iconic for "garden party" or "hostess" dresses from this time period.
**Video is Ai Generated and for inspiration only.
Measured Flat- double the bust, waist and hip:
Shoulder: 14”
Bust: 15”
Waist: 14”
Hip: free to 20”
Length: 50”
Excellent Vintage Condition