HopefullyLost gave good advice about people asking for money on the street. Many do in London where I live, especially at rail stations. I ignore them, otherwise their badgering could go violent. My advice to you is on seeing them, make sure you have an escape route and avoid eye contact. Cross the road if you can, or double back. Use your phone to contact a friend or dial for police assistance if you are threatened.

That said, whenever I see someone living rough in town and they are often with a dog for company, I'll buy them a KFC or a large burger, fries and a soft drink. Giving is an honourable thing as it feeds the needy. I would never give money as they could spend it on alcohol and/or drugs. Being a Londoner for many years I'm street-wise from having learnt Situational Awareness. Google it. You should find useful info for getting out of difficult situations, thus keeping yourself safe.