I am Sam and I am one of the UK tax experts here on Just Answer.
If you pass the charge on but it is incurred FOR the client AND you normally charge VAT then you pass the VAY charge on - these types of costs come under the remit of disbursements
But this is a cost incurred by your temp to attend to perform duties for the client so you do NOT charge VAT
See link here re VAT and disbursements for clarification
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