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Your friend will need to apply to the Court of Protection to become her husband's Deputy, if he has dementia and lacks full mental capacity.
To be honest, we Solicitors would normally charge more than £400 to deal with an application to the Court of Protection for someone to become a Deputy. Indeed the Court allow us to charge a client up to £850 plus VAT for such an application.
Therefore, unless your friend is happy to make the application without using a Solicitor, I think the quote of £400 is very reasonable.
If she is happy to do it herself, here is the link to the Court of Protection's website, which sets out all the indformation she will need to make the application.
I hope this assists and answers your question.
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