Hi. Does your dataset have data for multiple countries, or just the UK?
You will need a Country field in your dataset. In the dataset editor, create a geospatial hierarchy for Country. When creating the hierarchy select 1 country and United Kingdom if your data is for just one country, or select ‘…for multiple countries’ and the appropriate country field from your dataset. Then add Post Code to this hierarchy as well.
Your map should now show data correctly. (Here’s a related post).
Thanks,
Asem.