3 phase power supply to my w/shop/granny flat

[lotus 30]

I am thinking of running a new supply to my Garage w/shop I am 70+ years young I built my w/shop garage as a bungalow. I am thinking of later in life to convert it to a dwelling for us. I have 3phase power to the house. I did serve my time as a spark but went into refrigeration in my 20's so I am not up to speed with current regs. I am hoping that one of my kids will move into my house with a view to the garage being a granny flat. advice would be greatly appreciated on what will be required.
Andy