Not sure why you'd need a valid VAT invoice anyway as your clients won't be reclaiming any VAT on the supplier's invoice, they'll be reclaiming VAT off of your invoice which you have to charge regardless of what VAT (if any) the supplier might have charged. Any receipt/invoice should do if they simply want evidence of the costs you've incurred and are re-charging.
Also bear in mind if you're purchasing any services with the hotel/flights that would normally be standard rated in the UK, you may have to account for these purchases on your own VAT return under the reverse charge.
Also bear in mind if you're purchasing any services with the hotel/flights that would normally be standard rated in the UK, you may have to account for these purchases on your own VAT return under the reverse charge.
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