It will be intermittent. They need to "turn the tap on and off" to get a steady flow of people into the ICU. They explain it well towards the end of the latest BBC Coronavirus Newscast podcast episode.

Well, as I understand it, China live in an authoritarian state and we in a democratic one. Basically, when China said they were locking down, they absolutely did it and enforced it very strictly indeed. We haven't/can't do that quite so ruthlessly and so we've been given guidelines and advice and we (not most people I know but certainly the public as a whole) are flouting them. We will have restrictions put in place that will have to be adhered to strictly, but Boris Johnson is following advice from science officers and public health England over how best to manage a pandemic on what is essentially an island. These people are advising alternating strict and more relaxed rules depending on region and outbreak for a year or so. Because there's no vaccine yet and there's no way to provide for everyone getting this at once. If you can't fly in and and you can't sail in and you can't drive through the tunnel, you can't get here. Great Britain shares no land borders. So that effectively quarantines us away from the rest of the world. The science says most of us are going to get this. Strict and relaxed isolation measures would aim to control which region, to what extent and when in order to be more confident at providing essential life saving services for those who will need it. This won't be over in a few weeks. We may have a few weeks or even months ahead of us with a situation like Italy has right now, but if we pay attention to the advice and do as we are told, we may, IN THEORY, manage the rate of transmission and be able to better manage the entire impact of this.

Here's the link. The relevant bit is page 15
www.imperial.ac.uk/media/imperial-college/medicine/sph/ide/gida-fellowships/Imperial-College-COVID19-NPI-modelling-16-03-2020.pdf

There's not a date because the "off" switch will be when the number of people in hospital falls below a certain number. They do suggest that we'll be self-isolating for at least 2/3 of the time, unless we can come up with more efficient strategies that look at local numbers of cases.