I'm trying to get long mode no-op interrupt handlers functioning,

the handlers just echo the name of the handler to the screen
and return,

on enabling interrupts via sti I the first interrupt is always a
double fault,

if I make the code go into an infinite loop without returning from
the interrupt ie dont do iretq then the machine doesnt reset,

iretq resets the machine.

Now if I enable the interrupts and immediately after echoing
maybe 10 lines of text I switch interrupts off then
there is no interrupt not even double-fault,

so the double-fault doesnt seem to be caused by
the the code to setup long mode,

any ideas what may be causing the double fault?

I've read + reread the code and the 64 bit TSS looks correct,
and the IDT must be correct as it is echoing double-fault,

Correct is a very relative statement.

If you have a situation when you read, reread, rereread the code and see, that it's impossible that it don't work, then search for the problem in the places you're most sure of.

That's a general advice for OS-level programming, if you want specific answers, give some more details (ideally, the code).

well, on reading what you said I got an idea to try out!

uploading the code will be painful so I'll try the idea first,