It marks the highest rate since the Covid pandemic, official figures show.
Thirty councils across England now have to organise local polls after the government abandoned plans to delay.
Leader Nigel Farage says Reform is "the voice of opposition" to Labour, as he unveils his new top team.
Yellow weather warnings will also come into force on Wednesday across parts of England and much of Wales.
Patients and their relatives say there is a culture of abuse at a mental health hospital.