Hi there,
If you are looking for printing clothes or accessories, I will suggest you Tunetoo ;
Tunetoo
You can custom as you wish or find a logo from a designer (art shop).
If you are a designer or a graphist, you can also sell your designs :
https://www.tunetoo.co.uk/open-your-online-shop.php
I personally used this company for my friend's hen party t shirts, nice and quick.