I'm not convinced that Fuji is out of order here....it seemed a reasonable answer.
I thought the original question was "can I fly a single in the UK on my FAA license" - YES.
Can I night fly..NO.
Question now becomes "Do you want to night fly, in UK airspace, in a single engine piston aircraft?" If answer = yes, goto flying school and do Skill Test. If answer = no, goto same school and try to rent aircraft.