It looks like a wildflower I'm forever pulling up from all parts of the garden, so here it's a weed. Can't remember it's name off the top of my head. It gets tall, and has small pink flowers.

Epilobium perhaps. Related to Rose-bay Willow herb.

Just looked up all the willowherbs and the only one in Collins with shiny leaves is the small alpine one. Just joining in here to see the answer please.

I'm intrigued too! Definitely not Rosebay, that has alternate leaves, don't think it's an Epilobium either. Just noticed that there's a flower spike at the top, could it be a Veronica?