Even if they postpone 21/6, we'll still, presumably, remain at the current level of restrictions. So, assuming a third wave is actually happening, it's going to continue unless they roll back or even lockdown anew.
Of course all this is 'if' and 'maybe', but it's clear, IMO, we've opened too much too quickly. Again.
Its all about buying time for the vaccination program. Eradication has never been part of the plan and likely won't ever be. The real mistake was made a long time ago in not properly securing the borders. If the Indian variant (gamma?) had been delayed by a month or two from hitting our shores then the vaccination program would have been more advanced.
By extending the current restrictions it may be possible to bring the unlocking program in line with the vaccination program and without the need for rolling back on what we currently have. The whole thing just seems so precarious.