First of all, thank you for all the lovely comments about my finished cushion cover. I'm glad you like it!
Second of all, here, as promised, is the stitch pattern I used to make it. To crochet this stitch pattern you will need to know how to work front post trebles (also known as raised or relief stitches). This is not difficult, I promise - instead of crocheting into the top of a stitch you crochet around the post instead.

For the cushion cover I used an aran weight yarn (think this is equivalent to worsted) and a 5mm hook which resulted in a dense fabric with very little drape. Making a firm fabric was intentional on my part because I didn't want the cover to look gappy when stretched over the cushion. So depending on what you're making and your tension you may need to experiment with different size hooks and different weight yarns to get the effect you're after.
Terminology is UK. (UK dc = US sc, UK fptr = US fpdc).
fptr = front post treble (yrh, insert hook from front to back to front around stitch indicated,
yrh, pull up loop, complete as treble)
Crochet Cable Pattern
Make a foundation chain of required length, making sure that it is a multiple of 6 plus 3 extra.
Row 1: 1dc in 2nd chain from hook and each chain thereafter, turn
Row 2: 1ch, dc in each stitch across, turn
Row 3: 1ch, dc in first 2 stitches, *fptr around dc 2 rows below next stitch and each of next 3 stitches 2 rows below, dc in next 2 stitches, repeat from *, turn
Row 4: 1ch, dc in each stitch across, turn
Row 5: 1ch, dc in first 2 stitches, *skip 2 fptr, fptr around each of next 2 fptr from 2 rows below, then working in front of the fptr just made, fptr around skipped fptr stitches, dc in next 2 stitches, repeat from *, turn
Row 6: repeat row 4
Row 7: 1ch, dc in first 2 stitches, *fptr around each of 4 fptr from 2 rows below, dc in next 2 stitches, repeat from *, turn
Row 8: repeat row 4
repeat rows 5-8 until work is desired length.
God, I have no idea whether any of that makes sense! I hope it does but I appreciate that crochet patterns are often easier to understand if you are actually doing them at the same time as reading them. I took some photographs but I'm not sure they'd help much with interpretation either. Please let me know if it's just a load of gobbledegook and I'll see what I can do to make it clearer.
This stitch pattern is very adaptable. You could do the cable crosses less often, increase the number of dc stitches between cables, make the cable 6 stitches wide rather than 4, etc. If any of you try it I'd love to see what you come up with.
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Edited to add extra photographs for clarity (hopefully). Once again, this pattern is written using UK stitch terminology
Start with 2 rows of UK dc stitches...
Row 3: 1ch, dc in first 2 stitches, fptr around 3rd dc from row 1 and each of next 3 dcs from row 1, dc in next 2 stitches of row 2, and so on...
at the end of row 3 the work should look like this...
Row 4: 1ch, dc in each stitch across
Row 5: here we work the cable crosses... work 1ch, 1dc in each of first 2 dc of row 4, skip the first 2 fptr and work fptr around the 3rd and 4th fptr from row 3...
then, working in front of the fptr just made go back and fptr around the 1st and 2nd fptr from row 3, dc in each of next 2 dc from row 4... and so on
at the end of row 5 your work should look like this...
Row 6: 1ch, dc in each stitch across...
Row 7: 1ch, dc in each of first 2 dc of row 6, fptr around each of the fptr from row 5 working around the back two first, dc in next 2 dc of row 6, and so on...
at the end of row 7 your work should look like this...
Has this made it any clearer? I hope so...