I really wanted to get these, but there is no Lucy & Yak shop in London anymore, so I bought a tape measure to make sure I get the correct ones since I was also choosing from the petite range. Based on the measurements, I got a UK 8, which, mind you, I never ever bought such a size for myself, as it's too big for me, but based on the sizing chart, I even sized down as my measurements were in the middle between 8 and 10. The pants were enormous, and when I measured the waist at home, it was 10cm more than in the sizing chart. So I returned it and ordered UK 4 using the fact that UK 8 was way too big and even bigger than advertised. The jeans came way too small this time; I couldn't even put them on. They got stuck on my knees. Why is there like a 20 cm difference between size 4 and size 8? So inconsistent.
Don't even get me started on the length. I'm 158 cm, so right on the limit of your petite range, but I was dragging the jeans behind. But yeah, at least that can be altered.
Another thing, in the return portal, it never showed the available sizes like on the website, so I had to ask for the voucher and wait to receive it instead of submitting the refund along with choosing a new size for my pants. The size I wanted was clearly available on the website but not in the portal (happened twice).
I don't know where the sizing comes from, but it's widely inaccurate. I'm used to pants shopping being a nightmare, but this was next level.