By Janpled
Hertfordshire,
United Kingdom 
For identification please, these have turned up in my garden unexpecdly and grow to about 5 or 6 feet tall. They flowered in mid September
9 Oct, 2018
Answers
Helianthus for sure. Count the sepals. If 10 then possibly H. decapetala. But there are named ones with a double row as well.
9 Oct, 2018
Thank you both. I guessed it was a sunflower of some sort and you have confirmed that. It must have come from the bird seed we use.
9 Oct, 2018
looks like an helianthus but which one not sure. could be Jerusalem artichoke. see what other suggest.
9 Oct, 2018