I'm sorry that your question wasn't answered in a timely manner. It does sound as if Poppy is suffering from sundowner's syndrome - a form of cognitive dysfunction in dogs and people. It's conjectured that the dark and quiet of night magnifies the sensory loss in these patients which results in their anxiety and subsequent aberrant behavior. Other indications of cognitive dysfunction include disorientation, changes in social and interactive behavior - becoming "needier" or, conversely, more aloof - changes in locomotor and sleep cycle behaviors, and loss of "housetraining".
This is a progressive disorder and usually prompts euthanasia when owners are unable to control inappropriate behavior. If additional medical problems exist - brain tumor, e.g. - the onset of seizures may prompt euthanasia. You might find that a long-acting benzodiazepine such as clorazepate will be helpful for Poppy. Please consult her vet as to the availability of this or other benzodiazepines which have become more highly regulated in the UK and United States.
Ancillary care involves physically and mentally stimulating exercises such as swimming, massage, and range of motion exercises, encouraging relaxation, ensuring that Poppy is taken out frequently to minimize the cost of elimination "mistakes", encouraging re-establishment of daily cycles by feeding at regular hours and at least a few hours before bedtime, and administering a benzodiazepine before bed. Specialized diets rich in antioxidants may be of value such as Hill'sPrescription Diet b/d. The monoamine oxidase inhibitor selegiline(Anipryl) is the only drug licensed for use for the treatment of canine cognitive dysfunction in the States. Many of us aren't impressed with the studies supporting its use, however. Vivitonin is often prescribed in the UK. I'm similarly unimpressed with its value.
Cognitive dysfunction in dogs is just as difficult to manage as is Altzheimer's in humans. I wish I had some magic for Poppy. Please respond with further questions or concerns if you wish.