Can I ask how you know this and what you mean by a prolonged period of time? This is after all a data thread.
Prolonged period of time would be several weeks in a row, with hospitalisation numbers reaching levels that could overwhelm NHS.
You are right - I cannot predict the future with certainty but the trend so far indicates that case numbers can no longer balloon into stratosphere. The rate of growth is currently slowing down.
I have attached the screenshot showing how the case trajectory has evolved over past 2 months. Yes, cases have recently gone up but 11.7 million children going back to school with no bubbles/self-isolation requirements were not able to influence the transmission as much as the Euro 2020 fans. We are still running significantly lower than the July peak. With the slowing down rate of growth it is less likely that the Delta pandemic gets out of control (unless we see new variants or pandemic flu).