Yes. The weather forecast does appear to be severe in the midlands from next Monday.
Normally frost at night doesn't matter too much, at least for plants in a greenhouse, as the greenhouse is able to warm up during the day. However, in this case the daytime temperture is forecast to be around zero, with no sunshine. So temperatures in a cold greenhouse will become dangerous.
The forecast could be wrong. The Met Office does have a dreadful record for accuracy. And we don't know how long this cold snap will last, if it happens.
Personally, I intend to assess the forecast on Saturday and, if it still looks bad, then I shall bring a few seedlings and choice plants into the house for a couple of days.