So I recently bought a t-shirt from Primark, I picked up a UK size 10-12 (I'm usually size 10) and took it home before trying it on. As soon as I got home and tried it on, I thought it fit perfectly and the colour and pattern really suited me. Often I struggle to get t-shirts that are the right length, being a relatively tall person, but this one, contrary to the image below is surprisingly longer on the body than I expected.
Although, after a couple of hours of wearing it, I noticed the section that goes under your armpit was cutting in and the section across the top of the chest was restrictive. It was as if only the length and bottom half of the top had been designed for a UK size 10-12 and the upper part of the top had been taken from a UK size 6-8. However, because this top suits me so well and because I felt relatively comfortable in it, I have decided not to take it back and to keep it. The material is very light and suitable for summer and it complimented my pale skin tone.
If you see this top in Primark, I recommend you try it on and make sure you can move your arms freely and can take a deep breath without feeling restricted. From trying it on myself, I advise this clothing is for slimmer body shapes - although relatively slim myself, my broad shoulders didn't help with the fitting of the top.