There are still many people in vulnerable groups who do not have protection; neither directly (because they have not been vaccinated or because their vaccination has not prevented them from becoming infected then ill) nor indirectly from wider population immunity (because many younger age groups have not yet been vaccinated or infected).
The herd immunity threshold for Covid-19 with the B117 variant is unknown, but is likely to be high. Only around 79% of the population are adults, so even if coverage amongst them is 79%, only 62% of the population would be vaccinated. As the vaccines do not completely prevent transmission, the reduction in transmission that results would be expected to be lower than 62%7 . As a result, herd immunity is not likely to be reached in these scenarios without a further resurgence of transmission.
There are a very large number of older and more vulnerable people living in England. A small proportion of them will not be vaccinated and others will be vaccinated but would still be seriously ill, if infected. If many people are infected once restrictions are lifted, it is highly likely that many people will die or be hospitalised, though significantly fewer than in a scenario where vaccines had not been available.