We have set the admin to display both including and excluding VAT it shows on the catalogue but not on the actual product page.
Does anyone know where the code is for that?
Do you have a custom theme that outputs the price on the product page? There's only one setting for showing tax inc and excl in catalog. So if it's showing in the category page and not the product page it's probably a theme issue. You could test this by changing to a Magento default theme and seeing if it shows then.