This is the sort of bureaucratic nonsense that gives planning a bad name. Yes, technically the planners are within their rights to ask for a new application as the scheme now involves ‘new’ building as opposed to just conversion. But they could approve this change – which makes not one iota of difference to the end result – by way of a minor amendment to the permitted scheme. The latter process could, at a push, be done within a matter of days. Better still, they could just monitor your rebuilding to ensure it’s done correctly and, in the process, save themselves and you a great deal of time. However, taking on the council could indeed make it dig in its heels and so make things more difficult for you. Your best bet is to contact your local councillor and explain your predicament. Emphasise your commitment to preserving the building and try to get the councillor to bring pressure onto the planners to act quickly.