The UK is being singled out because its not able to import the groceries it used to do before Brexit now - there has been a low yield crop season in most parts of Europe and the domestic demand for groceries has literally exhausted the supply that can be exported. Since the UK is out of the Eu, its not possible to access the Eu domestic supply anymore and it has to wait for what remains for export.
https://www.cnbc.com/2023/02/28/british-supermarkets-are-rat...
There isnt such a situation like rationing vegetables anywhere else in Europe.