Two colourways of the one design for Charles and Diana's wedding. Sylvia over at Linens and Royals has a tapestry of the blue version. It features the Prince of Wales' feathers and the Spencer coat of arms.
I would guess that this was a kit or a charted pattern or both: the blue one above was described as a tapestry, the cream version cross stitch (and quite fine work which makes the detail stand out well and precisely). Magazine pattern? From an organisation such as the Royal School of Needlework? Don't know. It's a classic, elegant design that avoids being kitsch and would have required considerable time and skill to complete.
If you know the source of this design, or any other information, please leave a comment with any useful links you can provide.