Hello, I am Keith, one of the experts on Just Answer, and happy to help you with your question.
Any sales made in respect of this event would attract output tax, but as there is no entry fee these would likely be minimal; say you were selling drinks and other refreshments, for example. Any expenditure involved in running the event that bore VAT, that tax would be input tax, reclaimable on your quarterly return.
I hope that clears the air for you.
My answer is far from inaccurate, it merely covered the possibility of minor sales. If there are none of these then there is no output tax to be accounted for, but any input tax incurred in running the event is reclaimable.
However, if your organisation bills for items like colateral materials then such charges would be subject to VAT. If the customer was located in the States then the tax would still be chargeable, but at a rate of 0%; an export, a zero rated supply. I have consulted HMRC on such exports, actually to Switzerland, and this tax treatment was confirmed.