Ultimately, if you’re extremely difficult about it, I imagine they’ll probably send you to the dedicated overnight waiting gate at T3. You might think you’ve “won” if this happens - but in reality it’ll be very unpleasant.

Going through immigration is, technically, you applying for leave to enter the UK. Now I suppose there might be a way for an immigration officer to grant you leave to enter without you applying for it (or cooperating) but I can’t see them too excited about this.