The table isn't reflecting your updated source criteria because Clay doesn't automatically reprocess previously generated data. Even though the source preview shows the new filters, the table won't refresh until you re-run the step that generated the data.
To see the updated results with only London contacts, you have two options:
1. Delete and re-run the step that generated the data.
2. Duplicate the table with the updated source.
Either of these actions will apply your new source criteria and show only the London contacts in your table.