McKay's books include the Whitbread award winning Saffy's Angel, which has four sequels: Indigo's Star, Permanent Rose, Caddy Ever After, and Forever Rose. These are referred to as The Casson Family Books. The series focuses on an English family of artists, the Cassons. The children are called Saffron, Rose, Cadmium, and Indigo, and are named after paint colours (the large paint chart, which hangs in the Casson family kitchen, plays an important and recurring role in the books.) The parents' names are Eve and Bill. The first three books are written in the third person but focus on the point of view of the character in the title, whilst Caddy Ever After is written in the first person and is narrated by each of the siblings in turn, and Forever Rose is written in the first person and is narrated by Rose. Other characters featured in the books include Tom (an American boy who makes friends with Indigo and Rose whilst on a short stay in England), David (a thick skinned and well meaning reformed bully) and Sarah (or "wheelchair girl", as she was known to the Cassons before she met Saffron.)

Cadmium is the dreamer of the family; she loves animals and has an incredible amount of guinea-pigs and hamsters. She falls in love with her driving instructor, Michael, and it is she, initially, who looks after the other children. She loves her family, and often returns home to visit whilst studying Zoology in London. Saffron, or Saffy, is the realist, scornful, sarcastic, and fiercely intelligent. Really, however, she only wants to be loved; she often leans on her best friend Sarah for support. Indigo is the only boy, music loving and sensitive, and his best friends are Tom and David in the books. Rose is the true artist of the family, who loves her family. Eve is their ditzy mother who spends her time in the shed painting, when she isn't "hanging her young offenders" (she teaches them art on Saturday mornings) or painting murals in the local hospital. She hardly ever cooks a proper meal, so the children live on tinned food and Indigo's adventurous cooking, but she loves all her children and sees how special all of them are in their own way. Their father Bill is almost always at his swanky studio in London and is never home.

The order of the Casson Family series is as follows:

1. Saffy's Angel
2. Indigo's Star
3. Permanent Rose
4. Caddy Ever After
5. Forever Rose

McKay has also written many other books, including two other series, The Exiles and Porridge Hall

The order of the Exiles series is as follows:

1. The Exiles
2. The Exiles At Home
3. The Exiles In Love

The Porridge Hall books focus on Robin Brogan and his mother, who live in Porridge Hall on the Yorkshire coast. Once Porridge Hall was Mrs Brogan's family home, now it has been split into two houses, and she and Robin live in one half, from which Mrs Brogan also runs a Bed and Breakfast. The Robinson family live in the other half, and the two families are firm friends.

The Robinson children are the twins, Peregrine and Antoniette, who have abbreviated their names to Perry and Ant, their brother Sundance, and their sister Beany. Sundance got his nickname because Perry and Ant used to play Butch Cassidy, and Sundance was always the Sundance Kid. Beany, whose real name is Elizabeth, got her name because she declared, at a young age, that she wanted to be a bean when she grew up.

Other characters include Dan, a former enemy of Robin's, and later his best friend, and a mysterious girl called Harriet, who appears in the second book, The Amber Cat. Storytelling is a key theme in the second and third books, whilst beach combing and life by the sea feature large in all three books.

The order of the Porridge Hall series is as follows:

1. Dog Friday
2. The Amber Cat
3. Dolphin Luck

• The Exiles won the Guardian Children's Fiction Prize in 1992

• The Exiles At Home won the Nestlé Smarties Book Prize (Gold Award)(9-11 years category and overall winner) in 1994

• Saffy's Angel won the 2002 Whitbread Award

• Permanent Rose was shortlisted for the 2005 Whitbread Award

The Story of Bear

Happy and Glorious

Practically Perfect

The Paradise House books

1. The Treasure in the Garden
2. The Echo in the Chimney
3. The Zoo in the Attic
4. The Magic in the Mirror
5. The Surprise Party
6. Keeping Cottontail

The Pudding Bag School books

1. A Birthday Wish
2. Cold Enough for Snow
3. A Strong Smell of Magic