The General Canal Bye-laws only require port and starboard lights on certain commercial waterways - the Trent Navigation, the Weaver Navigation, the Aire and Calder Navigation, the New Junction Canal and the Sheffield and South Yorkshire Navigation. You would need them on most non-CRT rivers of course.
Otherwise the Bye-laws say:
10. lights and visual signals
Displaying of Lights and Visual Signals
(1) Subject as hereinafter provided, a power-driven vessel (other than a narrow canal boat) when under way at night shall carry –
(a) On or in front of the foremast, or if a vessel without a foremast then in the forepart of the vessel, and in either case at a height above the hull of not less than four feet, a visible white light so constructed as to show an unbroken light over an arc of the horizon of twenty points on the compass (225°) so fixed as to show the light ten points (1121⁄2°) on each side of the vessel that is, from right ahead to two points (221⁄2°) abaft the beam on either side; and
(b) in addition to the above light, at her stern a visible white light so constructed as to show an unbroken light over an arc of the horizon of twelve points of the compass (135°) so fixed as to show the light six points (671⁄2°) from right astern on each side of the vessel.
(2) A power-driven vessel, being a narrow canal boat, under way at night shall display in the forepart of the vessel, where it can best be seen and at a height above the deck or gunwhale or not less than one foot, a visible white light.
(3) A power-driven vessel (other than a narrow canal boat) when towing another vessel at night shall display:-
(a) Two visible white lights in a vertical line one over the other, not less than three feet apart. Each of these lights shall be of the same construction and character as the visible white light prescribed in paragraph (1) (a) of this Bye-law and one of them shall be carried in the same position as that light; and
(b) at the stern a visible white light of the same construction and character as that prescribed in paragraph (1)(b) of this Bye-law.