Billy garnett

Are there any National Insurance or VAT implications when making a payment to someone for speaking/ participating in an event our charity is holding. The speakers flight, accommodation and other related expenses are to be covered and there is a proposal to pay the participant what has been described to me as a modest "honorarium" or "stipend" of a few hundred pounds in recognition of them giving up their time to participate. This is voluntary payment that is not in return for a service and there is no contract for attendance and participation at the conference. Some of the speakers are domiciled overseas and some in the UK.