Out of our area, so apologies for that.
On 18th June, mainly on the coast between Snettisham and Hunstanton in Norfolk but also on some roadsides.
Puzzled that it had already flowered and set seeds. Also plants were obviously dying so that may indicate a biennial.
I wondered about wild celery but I'm not familiar with that, leaves though completely withered might suggest. My books unhelpful with plant at this stage in its life-history.
I grew up in Suffolk and my first thought was Alexanders, which is extremely common on the East Anglian coast. The seeds are distinctive and they look right: see here. It's a biennial as you suggest and the brown parts must be the withered male flowers.