Ziggurat

As part of a recognised pay dispute my employer refuses to accept partial contractual performance but instead "the [employer's] current position is that it will withhold 50% of pay. The 50% of pay being paid is paid on a voluntary basis by the [employer], without prejudice to its legal right to withhold pay in full and to its rejection of partial performance. This payment is being made by the [employer] as a matter of discretion and is not a payment in return for work carried out." Since this payment is an ex-gratia payment not made in return for any work carried out, and is less than £30,000, is it taxable? Thank you.