DTR 5.5 Acquisition or disposal by issuer of shares
An issuer of shares must, if it acquires or disposes of its own shares, either itself or through a person acting in his own name but on the issuer's behalf, make public the percentage of voting rights attributable to those shares as soon as possible, but not later than four trading days following such acquisition or disposal where that percentage reaches, exceeds or falls below the thresholds of 5% or 10% of the voting rights.
Additional requirements in relation to a listed company which purchases its own equity shares are contained in LR 12.4.6 R.