I believe BTI stands for Binding Tariff Information:
About Binding Tariff Information (BTI)
A BTI is a written tariff classification decision, given on request, which is legally binding on all Customs administrations within the European Community for up to six years from the date of issue.
BTI is intended to give you assurance about the correct tariff classification of your goods. It is not a legal requirement.
BTI decisions are made under the terms of Council Regulation (EEC)
http://customs.hmrc.gov.uk/channelsPortalWebApp/channelsPort...
http://ec.europa.eu/taxation_customs/common/databases/ebti/i...