Then you might want to look at this next:
where convert(varchar,DESPATCH_NOTE_DATE,111) >= @date
This expression means that any index on DESPATCH_NOTE_DATE can't help. Rather than converting DESPATCH_NOTE_DATE to match @date, do it the other way around: convert @date to match the datatype of DESPATCH_NOTE_DATE.
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden