Having owned 5 Lewin shirts for the last 3 years, I’ve just got 4 Tyrrwhit shirts and I can now compare.
I have to say that Tyrrwhit beats Lewin hands down. Well, almost.
They have way more choice, especially in non-iron. Not only in colours and patterns but you also get a choice of fabric weave, which is nice. They also let you choose arm length. The choice has allowed me to pick shirts that will work both casual and smart. I got to pick the cuffs too which I didn’t in Lewin.
The fabric is lighter, which might make it less durable, but it should be a blessing in the summer. My Lewin non-iron shirts are awful thick.
The fit is somewhat better for me in Lewin – this extra slim Tyrrwhit shirt still has a fair bit of room on the waist, but the arms are a little tight. I wouldn’t be able to get a good aero tuck on the time trail bike wearing this, whereas I would in the Lewin.
If these last as well as Lewin and genuinely don’t need ironing, then I’m sold.