Mrs May’s intervention comes as new figures show almost half of NHS trusts declared major alerts last week, while health officials fear worse may be to come from a surge in cases of flu.

The official data from NHS England reveals that 65 hospital trusts rose the alarm in the first week of January, signalling to nearby hospitals that pressures were becoming overwhelming.

One in six trusts issued operational alerts every single day last week, the figures show.

Cases of flu have risen sharply, latest figures show shows - and health officials believe the "flu peak" is still to come.

With cold weather sweeping across the country, there are fears of a surge in respiratory infections, as well as rising numbers of elderly people suffering falls in treacherous conditions.

In total, 65 of 152 trusts declared alerts warning that they had reached level three or four on a four-point scale. The previous week just 19 hospitals took such steps.

Under Mrs May’s plans, GPs will have to be open from 8am to 8pm every day of the week unless they can prove there is not demand in their catchment area.