Tourists/visitors from the United States usually do not need Advance Entry Clearance, also called a Visitor Visa. Be aware that as a visitor to the UK, it is against a violation of the terms of your visit visa to do any work or look for work.
If you have previously been refused a Visa, if you have previously been refused entry into the United Kingdom, or if you have a criminal record you will need to apply for a Visit Visa before you wish to travel to the UK.
If you are caught lying to gain entry to the UK, you could be banned, so please always follow the proper procedures. Americans (particulary young women) have had a reputation for lying to entry officers, so don't think you'll get a free pass. You may also want to bring proof that you have a job to return to.
Official FAQ from the United Kingdom Border Agency on Visitors: www.ukba.homeoffice.gov.uk/visitingtheuk/visitors/.
Cost: Currently the cost for a 6 month visitor visa (single entry or multiple entry) is $111 + postage fee.1
Timeframe for processing: It is always a good idea to apply for your visa BEFORE you make travel plans as it is not guaranteed that your application can be processed in a short amount of time. Most short visit visas are processed within 30 days, but it can be as long as 60 days.2
How to apply: Go to the UK Border Agency online application website. This can be found at www.visa4uk.fco.gov.uk/ and Register an account to start the process to apply for a UK visa.
If you have further questions we invite you to visit the UK-Yankee Online Forum and post in our Visas & Citizenship section and the friendly members there will do their best to assist you.
You can also seek professional advice & assistance. You can find an OISC approved immigration advisor at: www.oisc.gov.uk/people_seeking_immigration_advice/.
Please note that this information is current as of 05 Dec 2016.