So I transferred all my alterations to the pattern and then cut out a pair of jeans shorts. I sewed them up and tried them on before I added the waistband and the back still gaped!!! There wont be a yoke left at the rate I keep shaving bits of it.  I also scooped out the front crotch and once finished they all seem to be fine.
Details are on my diary thread but hopefully my next pair will be a breeze and will fit straight off 

When I hem the extensions to my son's t-shirts I first overlock the edge then turn it under and top stitch using a very narrow zig zag stitch - it almost looks like a straight line. As his t-shirts are mainly for work I don't bother with the double row of stitching. A good thread colour match is a good idea though.

I undid the top stitching yet again and scooped out the front crotch seam as I thought that was the problem - it was!! I then re-topstitched that seam and the back seam. I made the belt loops and sewed the waistband on. I baulked at any more topstitching today so I'll leave that till next time. 

Thanks for posting that @Sara-S. I enjoyed looking at all the quilts. What a good array you had. 

I did my stint this morning as I was shanty singing this afternoon. I disassembled and reassembled part of my jeans as i wasn't happy with the fit. Feels better now but still a tad roomy.

I finished my jeans but the waist was too big. I thought I could wear them with a belt but then decided they needed taking in so I undid the waistband at the back and unpicked the top stitching down the centre back seam, i then removed the excess, resewed the cb seam re top stitched and redid the waistband.
The hardest part was lining up the new top stitching with the previous lot. They fit a lot better now.
I've added a pic of the new back which I'm quite pleased with.

That is fascinating @Sara-S! I never knew such stuff existed. Every day is a school day 

Oooh, I like that @Stitches.