wow lots of Brit generalisations on this thread !
We usually tip between 15 -20% sometimes more on a sit down meal. We always give a few extra dollers to delivery takeout. I dont usually tip for takeout that I pick up because you are not tipping for the food your tipping for the service so I don't consider it necessary then when all they are doing is handing you a bag.
Usually tip hairdresser between 15 -20% depending on how happy I am, last time I went I only tipped 10% because I wasn't at all happy with it.
Oh and I don't tip my dentist but my teeth are good and so are my kids