Some relevant info here:
Length of night work. An employee working nights must not have their average normal hours of work exceed eight hours in each 24-hour period.
Night workers are entitled to receive free health assessments.
Rest periods. An employee is entitled to a minimum of 11 consecutive hours rest in each 24-hour period. An employee is entitled to a minimum of: one uninterrupted rest period of 24 hours in each seven-day period; or two uninterrupted rest periods of 24 hours in each 14-day period; or one uninterrupted rest period of 48 hours in each 14-day period.
Rest breaks
An employee is entitled to a rest break where the working day is more than six hours.The rest break should be a minimum of one uninterrupted period of 20 minutes.During the rest break, an employee is entitled to leave their work station.The rest break cannot be at the end of the shift.
So maybe he should complain that his 20 minute break was interrupted. It seems wrong that there is no agreed time for breaks or recording of breaks. To cover himself in future he should formally notify someone he is taking his break or at least fill in a register then there can be no misunderstandings if a problem arises again.
And yes, as a night worker he is entitled to a free health assessment.
This may help
http://www.direct.gov...ndTimeOff/DG_10029451