absolutely still legal - the requirement is only one aspect of the suspended sentence - there is also the requirement that no further offences are committed during the operational period (i.e. the period the term of imprisonment was suspended for)
obviously if the probation service never bothered to organise the unpaid work or supervision elements, instead of having that hanging over you, you have could to go back to court and apply to have the order varied so you are not always worried that the requirement will come back to haunt you!