A while ago Prior Notification was extended to 30th May 2019. That is still the case - nothing has changed, except that time marches on. This leaves you a window of one year and three months which suddenly does not sound like a huge amount of time to apply and get your extension completely finished by this date.
Prior Notification provides enormous benefits for the homeowner in terms of the size of rear extension that can be built providing that your neighbours are in agreement. Under Permitted Development a rear extension of 4m can be built for a detached home, and 3m for a semi-detached or terraced home. Under Prior Notification this doubles to 8m and 6m respectively.
So if your home is bulging with children, teenagers, ageing relatives or your hobby or general lifestyle, now is the time to get Prior Notification to work for you.