In my view, these costs are disbursements, as opposed to charges for a service, and as such can be passed on 'as is' without being part of my VAT calculations. This is largely based on "VAT: costs or disbursements passed to customers", https://www.gov.uk/guidance/vat-costs-or-disbursements-passed-to-customers
To take electricity as an example. I pay for electricity (using none myself), split is between the leaseholders and bill them for their share. Is this a disbursement for VAT purposes?Disbursements: costs to exclude from VAT calculations
A payment made to suppliers on behalf of your customers is called a ‘disbursement’ if you pass the cost on to your customers when you invoice them.
You might be able to leave out these payments from your VAT calculations because it’s the customer, not you, who buys and receives the goods or services; you’re just acting as their agent.
To treat a payment as a disbursement all of the following must apply:
you paid the supplier on your customer’s behalf and acted as the agent of your customer
your customer received, used or had the benefit of the goods or services you paid for on their behalf
it was your customer’s responsibility to pay for the goods or services, not yours
you had permission from your customer to make the payment
your customer knew that the goods or services were from another supplier, not from you
you show the costs separately on your invoice
you pass on the exact amount of each cost to your customer when you invoice them
the goods and services you paid for are in addition to the cost of your own services