Data processing apparatus comprises vector processing circuitry to apply a vector processing instruction to data vectors having a data vector length, each data vector comprising a plurality of data items equal in number to the data vector length, the vector processing circuitry having circuitry defining a plurality of processing lanes, there being at least as many processing lanes as a maximum data vector length; and control circuitry to selectively vary the data vector length used by the vector processing circuitry amongst a plurality of possible data vector length values up to the maximum data vector length and to disable operation of a subset of the processing lanes so that the disabled subset of processing lanes are unavailable for use by the vector processing circuitry and there remain at least as many enabled processing lanes as the data vector length set by the control circuitry.