If there is only one delivery address on your order, and you have chosen Named Day or Next Day delivery (i.e. a specific date), all your items will be dispatched on the same day. Some of your items may be fulfilled by different warehouses, however, they will still be dispatched and due to arrive on the same day.
If you have chosen Standard delivery for your order (no specific day, on or before a certain date), all your items should be dispatched on the same day. However, if some of your items are dispatched from different warehouses, or require additional processing time (i.e. for personalised items), they may arrive on different dates - but still within the quoted delivery time frame.
We state in all our dispatch emails "Please note that some of your items may be delivered separately. In such cases, we will always send you a separate tracking email for each delivery."