You're perfectly entitled to take pictures of who you like, and what you like, as long as you're in a public place (or a place where the owner has granted you permission for photography).. There are a few very limited exceptions (covered by such varied legislation as the Official Secrets Act and the Sexual Offences Act), but they won't apply to you.
However, since you're planning on offering a service for payment, you would almost certainly need a street trader's licence from the local authority. Most authorities have very strict rules about issuing such licences (especially in seaside towns where many people would like to trade) and I suspect that your application would be refused.
Chris