These are books originally published in the US that were also published via UK publishers, listed by publisher:

Egmont

• Two Boys Kissing by David Levithan

Faber & Faber

• Highly Illogical Behavior by John Corey Whaley

HarperCollins

• Boy Meets Boy by David Levithan
• Lies We Tell Ourselves by Robin Talley

Hodder

• Ash by Malinda Lo
• Girls of Paper and Fire by Natasha Ngan

Hot Key Books

• This Book is Gay by Juno Dawson

Macmillan

• You Know Me Well by David Levithan and Nina LaCour
• Carry On by Rainbow Rowell
• Fans of the Impossible Life by Kate Scelsa

Penguin

• Simon vs. the Homo Sapiens Agenda by Becky Albertalli
• Leah on the Offbeat by Becky Albertalli
• The Miseducation of Cameron Post by Emily Danforth
• Will Grayson, Will Grayson by John Green and David Levithan
• Jack of Hearts (and other parts) by L.C. Rosen

Simon & Schuster Children’s UK

• What If It’s Us? by Becky Albertalli and Adam Silvera
• More Happy Than Not by Adam Silvera
• History is All  You Left Me by Adam Silvera
• They Both Die at the End by Adam Silvera
• Infinity Son by Adam Silvera
• Odd One Out by Nic Stone

Usborne

• If I Was Your Girl by Meredith Russo
• Birthday by Meredith Russo

Walker

• I’ll Give You the Sun by Jandy Nelson
• Release by Patrick Ness