I want to shorten postcode information in a cell to only show the first or first and second letter. i.e. WF17 would show WF only or S17 would only show S. The range of cells will have a mix of 1 character and 2 character postcodes so I would need the formula to cover both scenarios.

What have you already tried? We help with specific problems, but we are not a codewriting site. – harrymc Feb 14 at 17:57
I found a not so elegant solution.
So, if you have A1,A2 etc filled with codes that start with either 1 letter or 2 letters in another column, do the following. In B1 type
=VALUE(MID(A1,2,1))
Use autofill for the rest of the cells in B and you should have either a number or an error. Now in C1 type
=IF(ISERROR(B1),LEFT(A1,2),LEFT(A1,1))
Autofilling the rest of C should give you what you needed :)