The requirement to register a combustion plant and the requirement to have a permit for it to operate are different things and need not be permanently linked. In the case of hire boilers, it would be reasonable to require the hire companies to register all their boilers at the appropriate time by supplying the available information in the tables below (from Annex 1), and this should be free of charge. It would then fall to the person wishing to use a registered boiler to apply to vary their permit for their site to include the temporary plant for the relevant period (as in a hire car being registered with DVLA but temporarily operated by a licensed driver). If a permit did not exist for that location and/or that operator, a new permit would be required to operate the temporary boiler; in emergency situations his could cause some logistical difficulties and retrospective applications may need to be considered.