Circa 1960's or 70's Welsh Guards 2 Yard flag. It is marked 2 Yard and has a makers label for a known maker of Welsh Military (& other) flags who were based at East India dock Rd in the 30s and 40's, though I don't know when they moved to Balham Rd. Obviously the Queens crown makes the flag post 1953.
One side of the design is in reverse, which seems odd considering the WG logo is constructed of two separate pieces sewn either side of the main guards flag. To me it would have made more sense to just have the same center piece on both sides, though perhaps there is a reason for this.