If you might have more than 999, you can just do:
=SUMIF(A:A, "Wickes", B:B)
Although, what I'd do is:
Copy column A to Column D. Select column D, Data -> Remove Duplicates, then Column D will just have each one listed once.
Then in E1 put =SUMIF(A:A,D2,B:B) and copy that down.