Monster weed

Monster weed

Observation - Monster weed - UK and Ireland. Description: This sowed itself in June/July and it is now late September and it is over 6 feet tall and still growing and hasn't flowered. It is branching at every leaf node and the base of the stem is 2 inches across. No discernable hairs on the leaves and the leaves

This sowed itself in June/July and it is now late September and it is over 6 feet tall and still growing and hasn't flowered. It is branching at every leaf node and the base of the stem is 2 inches across. No discernable hairs on the leaves and the leaves are straight onto the stem, almost wrapped around in pairs.
It is perhaps something from a bird seed mix but it is nothing listed on the packet so maybe not. It is not Himalayan Balsam. Any idea what it is?