Why have cells in Calc stopped processing decimals?

In the last 48 hours some cells on my Calc sheet have stopped calculating any figures less than a pound. e.g. a column total of £163.47 will change to £164.47 if I add into the column a figure of £1, £1.20. £1.35 etc. It’s rounding the pound value up or down but not changing the pence. Any ideas please?

Crystal ball is broken. Please upload / make your document available (after having replaced sensitive content). I upped the question so you should be able to attach the file.