From the Trade Union and Labour Relations Act;
(1) An employer shall permit an employee of his who is a member of an independent trade union recognised by the employer in respect of that description of employee to take time off during his working hours for the purpose of taking part in—
(a) any activities of the union, and
(b) any activities in relation to which the employee is acting as a representative of the union.
(2) The right conferred by subsection (1) does not extend to activities which themselves consist of industrial action, whether or not in contemplation or furtherance of a trade dispute.
Perhaps the outcome of the full hearing will depend on whether the judge feels that DH was taking part in industrial action when he refused to work.
Dave