If I want to fly night VFR in a G-reg aircraft I require a JAA conversion with night rating, if I want fly night VFR in an N-Reg aircraft I can, no problem. At the end of the day, it all comes down to what letter is on the side of my plane...
The ANO states that you are not allowed to fly in controlled airspace that require compliance with IFR rules.
So you can fly at night outside of controlled airspace under IFR rules and in controlled airspace under an Special VFR clearance on your FAA PPL in G-Reg aeroplanes as long as you have a current FAA IR (which of course you don't yet).
From what I understand the above is valid worldwide in G-registered aeroplanes on the basis of your FAA PPL (and a current IR if you wish to fly at night) as the ANO doesn't limit the automatic validity of ICAO licences to any specific area (i.e. UK).