Non-UK residents can reclaim VAT by applying for the relevant form from:

HM Customs and Excise
VAT Overseas Repayments Unit
Customs House
PO Box 34
Londonderry, BT48 7AE
Northern Ireland

The completed form must be sent back to the above address, with proof of the VAT paid. Delegates will be issued with VAT receipts at the conference.

See here for more information: Applications for refund of UK VAT by EC & non EC businesses