In England and Wales you can write your own Will.
However there are many traps for the unsuspecting person which could result in estate assets passing to persons not intended to receive them, either because key Will provisions are invalid, or because the person’s choice of words runs foul of a legal rule or principle of which the writer was unaware.
The best advice is to rely on a professional Will Writer to take your instructions and translate them into legally effective provisions in your Will.