Somewhere Like This by Pat Arrowsmith

The blurb on the back:

All girls together...
Collingwood Prison - where the bad girls go. Where the only love and sex available is of one kind. Where every woman is either 'butch', 'fem' or 'straight' - and there aren't many who are straight.
Somewhere Like This is the story of a group of Collingwood prisoners and their love-affairs: butch Lorry, the young burglar who wishes she'd been born a boy... Mavis, fluffy, feminine and confused... and upper-class Jan who knows exactly how get what - and who - she wants...
Pat Arrowsmith's novel of life in a women's prison is remarkable for its honesty; it could only have been written by someone who has observed life 'inside' from the inside.