I have several textbooks for A level biology and one of them says that plant cells don't have lysosomes, but that their vacuole fulfils this purpose instead. Another textbook also hinted at this by labelling lysosomes in a diagram for an animal cell but not for a plant cell. Is this true? How would a vacuole fulfil the purpose of lysosomes- don't they only contain cell sap, or do they have digestive enzymes too?

Much appreciated

It depends a bit on your definition. Plant cells, as you mention, contrain vacuoles, which like the lysosomes in animal cells are membrane-bound vesicles within the cell. These certainly share some properties with lysosomes, and indeed in some cases they've been found to contain hydrolytic enzymes, which means they're essentially performing the function of a lysosome. So you could think of them as the plant's 'lysosome'.

Plant vacuoles do have other functions, though, including water storage and maintaining hydrostatic pressure in the cell, and tend to be significantly larger. Overall they're different enough from animal lysosomes that they're considered a separate organelle, though they have some things in common.