If you do not transpose one array your formula will calculate:
=SUMIFS(YTD_GBP,Region,"Central Budgets",Cost_Desc,"Hardware",Non_Billable_Project,"Non Billable")
+SUMIFS(YTD_GBP,Region,"Corporate Services",Cost_Desc,"Hardware",Non_Billable_Project,"Central Budget")
/1000

If you transpose, calculation will be:
=SUMIFS(YTD_GBP,Region,"Central Budgets",Cost_Desc,"Hardware",Non_Billable_Project,"Non Billable")
+SUMIFS(YTD_GBP,Region,"Corporate Services",Cost_Desc,"Hardware",Non_Billable_Project,"Non Billable")
+SUMIFS(YTD_GBP,Region,"Central Budgets",Cost_Desc,"Hardware",Non_Billable_Project,"Central Budget")
+SUMIFS(YTD_GBP,Region,"Corporate Services",Cost_Desc,"Hardware",Non_Billable_Project,"Central Budget")
/1000