I read this sometime around 1989, borrowed from a public library in South London.
It takes place in the summer of 1976 during a heat wave. It starts with a happily married woman looking for a button that fell off her son's school blazer. She finds it and puts it in her coin purse. Then she starts baking a chocolate cake for her daughter who's coming home from uni. She lives in a cul de sac called Home Farm Close. The daughter turns up with a male friend and they all sit in the garden. Mum goes to her bedroom to change out of her sweaty clothes and who should pop in but the male friend looking for the loo.They have sex (as you do) to the backdrop of the conversation in the garden coming through the open window… (Well it was the 70s.) The mum moves out of her home and into the male friend's squat and tries to domesticate him by having dinner parties and suchlike, but no-one turns up. At one point she bakes a cheese (?) souffle. Then she finds out she has cancer. It ends with her dying in hospital and the nurse finding the button in her coin purse.
Does this ring any bells for anyone?