You're right that Skymap isn't certified. It would therefore be illegal to run it on a permanent power supply from the R44 bus. It would also be illegal to have the unit permanently fixed to the aircraft with screw or rivet holes made in the aircraft's metalwork.
However, plugging it into the cigar lighter socket and having it mounted on a suction RAM mount inside the screen is OK.
It can run on batteries - but it needs mega-power and so the batt pack is bulky.
Probably better off with a Garmin 296 or 496 with some decent UK airspace upgrades which are available free over the internet. You can download the London heli routes, high obstacles and helicopter landing sites from
here