When the first signs of Dementia appear it is imperative to put your health and financial affairs in order.
Initially you will probably be in full control of your faculties but as time progresses you will begin to lose control of your mental and physical abilities.
To ensure your affairs are put in order the two important documents you should complete are a Will and a Lasting Power of Attorney. Any professional person who helps you to prepare these documents will have to satisfy themselves that you are sufficiently competent to provide the instructions.
The worse Dementia becomes the less competent you will become and without those documents in place your affairs may have to be administered by the Court of Protection at considerable cost to your estate.
The advice then is to act as soon as the onset of Dementia is diagnosed. Delay will be expensive and not necessarily in accordance with your wishes