With much gratitude to Jimi and Marsha (who allegedly first released a pair into the wilds of west London!) Linda, Mum-in-Law and I waited patiently in the car park at ASDA, Slough (on Thames!) for a vast roost of Ring-necked Parakeets to form. By the time it grew dark and the flock dropped down from the 'interim roost' onto bushes by the M4, I reckon around a couple of thousands had gathered.
I still find the sight and sound of these exotic birds an enjoyable experience, especially when Windsor Castle is on view in the opposite direction!