Why is this downvoted? I've only been to London once, but I can certainly speak to identical behavior from panhandlers at many intersections in central NC, USA. They'll hold signs pleading all sorts of sad stories, typically asking for finances for food. Sometimes faking limps or missing appendices (one time I could clearly notice the guys leg tucked up inside his jeans...)

If you offer to buy them a big meal at the restaurant down the street, they'll cuss you out and harass you. Then promptly heckle the car behind you for cash.

They want cold cash for drugs, nothing more or less. Many of these folks run it like a job, panhandling for 4-8 hours a day, then hopping in their car and returning to their shared living situation to shoot/snort/smoke up. It's a racket than can easily generate more income than an honest hourly job around here.

It's really quite sad, because amongst them are some folks who seriously need help, and would be nothing less than extremely thankful for any food or clothing provided to them. Sadly, the druggie gremlins are in the majority, so I don't give anything to anyone. Lock the doors and look straight ahead. I keep my hand near my firearm too, because I've had them vigorously pull my car doors before.