Weird registration of mystery

[quicksilver]

Can anyone shed any light on this weird reg I've just seen this afternoon?

That's a standard UK plate but FSS 1701 is not a UK format and doesn't appear on the DVLA database. Google reveals nothing so what the heck is it? At a guess maybe a special for the US forces like UKAX but it doesn't seem to be documented anywhere.

I have seen one other vehicle on an FSS reg. This one has a non-standard font on the front but standard on the back, as well as looking like it's been pulled out of a hedge. Interestingly this is a much higher number (but also ending 01) despite being an older vehicle. Anyone know what's going on here?

  

[Spiny Norman]

Is it not an NI plate? 

 

[Marina door handles]

Isn't that a Northern Irish layout number plate? Three letters and then 4 numbers is the norm I think.

 

[quicksilver]

Nope, it's not Northern Irish as they all contain I or Z. Three letters and four numbers has never been used in mainland GB so it's not a valid format for a normal UK reg.

[adw1977]

@LightBulbFun is usually the expert on such matters.