This was the question for the Court of Appeal in the case of ICTS (UK) Ltd v. Visram  EWCA Civ 202. Mr Visram had been employed by American Airlines before his employment transferred to ICTS. His contract of employment included long-term disability benefits. The benefits were set out in a booklet, which stated that the payments would continue until the earlier date of "your return to work, death or retirement".
A new Equal Pay bill has been put before parliament. Supported by the equality group the Fawcett Society, it would give employees the ability to make a "right to know" request obtain information related to pay of a comparator. The information which could be requested would potentially include salary, benefit, bonus, overtime, allowances in respect of shift working and standby time, bank holidays and time off in lieu, attendance pay and performance related pay. There is also proposed to be a less specific catch all of "any other terms related to equal pay". If an employee was requesting information about something which was not a contractual term (entered into between the employer and the comparator) the provisions propose that the employer would make a statement to that effect.