There are two types of SIA licence:
A front line licence is required if undertaking licensable activity, other than key holding activities (this also covers undertaking non-front line activity). A front line licence is in the form of a credit card-sized plastic card that must be worn, subject to the licence conditions.
A non-front line licence is required for those who manage, supervise and/or employ individuals who engage in licensable activity, as long as front line activity is not carried out - this includes directors (For the purposes of the Private Security Industry Act 2001, "director" means executive and non-executive directors, shadow directors, parent company directors and corporate entities holding a directorship) or partners. A non-front line licence is issued in the form of a letter that also covers key holding activities. If you have a non-front line licence you do not need to have another one if you are involved in another area of non-front line licensable activity (for example: if you are a director of a firm supplying security guards but you also supply vehicle immobilisers, you will not need to have two licence's).