Several designers have jumped on the bandwagon of the Union Jack's popularity as a design icon and created kits for tapestry, needlepoint and cross-stitch.
I wouldn't be surprised if it reappeared in their range.
Jacqui Pearce of Granny Knits has several Union Jack (and other British-themed) designs using cross stitch and tapestry / needlepoint, such as those below.
A beginner's cross stitch kit (link)
This is a detailed kit, the filigree work is all tapestry stitching, red aqua and white. Find it here.
Jan Constantine has used the Union Jack in a multitude of her designs - click here to see her British collection (made designs, not kits). She also has some kits, including this one.
It is sold as a tapestry kit here, and also as a downloadable pdf.
There was also a Jan Constantine Union Jack cross stitch design in Cross Stitcher magazine, issue 226:
This issue turns up for sale on eBay from time to time.
This Anchor brand tapestry kit can be regularly found on eBay. I don't like it as much, as it's hardly subtle: (it doesn't, to me, stand up against the designs I've shown you above. But I'll include it here to record its existence).
I've also seen a number of patchwork quilt designs employing the distinctive geometry of the Union Jack in quite a variety of fabrics and colours.
The 2012 London Olympics will no doubt be inspiring more designers to create patriotic works. If you know more links, please leave a comment with them - especially for kits/patterns, not finished works, as the focus of this blog is handwork done by individuals rather than mass-produced patriotic items.