It's been said before, but to qualify for the CIL exemption you have to follow a strict process. Including notifying the council of your commencement date.    Well apparently the regs on this are contradictory....   https://www.theguardian.com/money/2019/jan/27/a-24000-penalty-for-failing-to-submit-one-piece-of-paper-to-the-council     Best file a commencement notice anyway.