This part of GOV.UK is being rebuilt – find out what beta means

HMRC internal manual

Stamp Taxes on Shares Manual

CREST: CREST Functionality: Trade System of Origin (TSO)

The Trade System of Origin (TSO) is used to indicate the trading venue, (e.g. the LSE or a multilateral trading facility (MTF)), upon which a share transaction was undertaken. Each trading venue will have its own unique TSO code which is allocated by CREST.

The TSO field is a mandatory data field that must be completed by all principal broker dealing organisations. This is because the TSO code is used to determine whether a purchase of securities on that exchange on a principal purchase is eligible for intermediary relief (see STSM042050) or stock borrowing/lending relief (see STSM042130).