An Important tip!
''Tipping', gratuity or 'service' is handled very differently in the UK and America. It's important to get this right when you visit each place as it can affect whether the staff in bars, cafe, restaurant, hotels, hairdressers, and the drivers of taxis or buses think that you are lovely, rude, strange, or whether they chase you down the street!
In the UK...
In the UK the reason for tipping is to show that you really liked the service. In the UK we have a high minimum wage, and no-one can be paid below this amount for any work, so when you tip, it is mainly showing politeness to the service person, and to acknowledge that they did an excellent job.
You can tip more or less depending on how good you thought the service was, and the average tip is around 10-20%. So if you loved your new 50 pound haircut, you should add another 5-10 pounds onto your bill, and this will go directly to the hairdresser! If you didn't like the service, don't tip! This is the case even if 'service' has been added to your bill. If you didn't like the service, you can always refuse to pay. Or if you are a student, traveller on a budget, or simply can't afford to, it's also ok not to spend the extra money.
In the US...
In the US, you will often hear 'tips' called 'service'. It is essential to tip in the US, because the waitresses, bar staff, maitre'd's in these industrys are paid a low wage which they cannot afford to live on, and therefore your tip is much needed by them.
It is actually part of the payment that you make and very often is not optional! Especially in restaurants, if you do not pay the service, you have not paid your entire bill, so watch out!