Bromopsis inermis Hungarian Brome DD I
The other sub species according to Stace is only known from one site in Essex so I'm fairly sure that this introduction must be ssp inermis. Hungarian Brome was at one time used a fodder crop so you might expect it to appear from time to time on country verges. We had intended to stop on a very narrow road to look at this plant more closely but I took this photo just by winding the car window down.
This plant has escaped into much of England and lowland Scotland but there is little to be found in northern Scotland, Ireland or Wales.