How to declare reimbursements

I am a self-employed delivery driver for an online platform. It works different to most delivery platforms in the way that you are given a shopping list and you are the one to go and carry out the shopping with your own money. After you deliver the order you are paid a delivery fee and also reimbursed for the items you bought with your own funds. This payment is sent as one however on the invoices from the company the amount is clearly broken down into two parts - how much you were reimbursed for the items and how much you were paid for carrying out the delivery. It also says on the invoice that I am supposed to pay tax on only the delivery pay. I'm confused as to whether to collect all the receipts and declare my earnings as the full amount they send me (delivery pay + reimbursement) and then also declare the receipts as expenses or only declare my earnings as the delivery pay and not claim expenses on the shopping costs. I am worried that the first method would cause me to go over the VAT threshold. Thanks for any help in advance

Hi,
You declare all the income as part of your turnover and then deduct the cost of the shopping as the expense.
Thank you.