Mr Fizzion wrote:
I found some old iron pipes that had been left rolling on my dining
room ceiling by a previous plumber. They are far too long to get out
without cutting them or taking up all the floorboards.

I have tried a metal cutting blade on my jigsaw but progress is
*extremely* slow - the pipes are thick walled and very hard.

Will an angle grinder with appropriate cutting disk do the job...I
don't actually have an angle grinder otherwise I'd try it. (I've never
used one before)

An angle grinder would be fine, as would a jigsaw. With the angle
grinder, lots of sparks will be produced that may set fire to
inflammable junk such as sawdust, shavings, spider webs, old felt
lagging, that may be under the boards, so take care. Also angle
grinder sparks will ruin any glass or ceramic surface they hit,
so watch out for your mugs/windows/glasses. First support the
pipe, so it won't fall and bash the ceiling when you cut it. Get
the grinder going, then tough the wheel on the pipe. When a small
slot has been made, rub the wheel back and forth to assist fast
cutting. Do not let the wheel chatter in the slot, or wiggle it
sideways, or the wheel will wear rapidly. Should the wheel bind
(jam) when cutting the pipe, the grinder will give you a big jerk,
so be careful. Don't run the grinder where any of your flesh could
get in the way. Careful of electric/gas/other water pipes.