In article ,
Ian Jackson wrote:
This has been growing for some time in the 'wild' part of my garden
(photo here):
https://ibb.co/TgtjQj7
It's presently around 4' 6" tall, and looks like a dark green spiky
thistle. However, there is no sign of any of the usual thistle seed
heads. Can anyone tell me what it really is?

A thistle. Until it at least starts to flower, I can't guess further.
There are several genera called thistles, some of which are cultivated.
I would leave it until it starts to flower and then decide.


Regards,
Nick Maclaren.