To incorporate a private company limited by shares you will need:

A registered address in the UK (no PO BOX accepted)
Details of all physical people that will act as director and/or as shareholder. 1 director and 1 shareholder are mandatory, and at least 1 director has to be a physical person.
Number of shares to be issued: the company can be created with any number of shares, for any amount, in any currency.
To incorporate a private company limited by guarantee you will need:

A registered address in the UK ( PO BOX not accepted)
Details of a physical person that will act as director. It is mandatory to have at least 1 director
Details about the members and the amount guaranteed for each of them.