Another voice of reason, I hope. I presume Table1 has more than just those 2 fields.
Don't save Table2 Area2 (ward) data into Table1. Build query that joins on the common PostCode fields to retrieve related data. This is a primary reason for using relational database.
If you want to see the Ward next to PostCode on a form, options:
1. pbaldy suggestion using a multi-column combobox for selecting PostCode, then textbox can reference combobox column by its index, index begins with 0: =[cbxPC].Column(1)
2. include Table2 in form RecordSource (RIGHT JOIN) and bind textbox to Table2 Area2 and set Locked Yes and TabStop No
3. DLookup() expression in textbox