Use a shortcode to display the uk food standards hygiene rating for the current business (current post's title) or you can pass the business name within the short code.
This plugin calls and uses the UK food hygiene rating data API, see:
http://ratings.food.gov.uk/open-data/en-GB
Install plugin via the usual plugin method
Activate the UK Food Hygiene Rating plugin
Include the [food] shortcode in your post and plugin will use the post's title as business name to look up
Or use [food business="the business name"]
Configure the plugin via the plugin's Settings admin page