The Trust has released a statement saying Maria Ball has resigned with immediate effect.
The process for appointing a new or interim chair will be started immediately but in the meantime Paul Remington who is vice chair will lead the organisation with Andrew Morgan, the interim chief executive.
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Rain and blustery winds will spread across the region this evening but it will turn clearer later in the night. Further showers tomorrow.
There are now more hospital admissions than ever before due to obesity. A survey found Hertfordshire had the most admissions.
There'll be a few showers about at first this afternoon but they will ease later before more prolonged rain arrives in the evening.