I am a US citizen and have recently visted the UK with simply a passport which allowed me to vist for 6months I have heard rumors that I am obligated to stay in the US for a Equal amount of time that I have visited the UK before I am able to return, but I am struggling tour no any proof of this obligation .. Am I missing somthing or is it simply not true
The Home Office has prepared a set of substantially revised visitor rules which will be laid before Parliament this Thursday (26 Feb 2015). The new rules, along with the new guidance, will answer questions like yours with much more clarity and resolution than the current rules/guidance. The rules will be unveiled on the Hansard site this Friday (27 Feb 2015) and activate in April. The Home Office site will be updated during March.
The new guidance will state flat out...
There is no specified maximum period which an individual can spend in the UK in any period such as “6 months in 12 months”.
That should put a lot of internet lore on the subject to rest. What they WILL say is something along the lines of...
if it is clear from an individual’s travel history that they are making the UK their home you should refuse their application.
Paragraph 41 of the Immigration Rules, which states in part...
intends to leave the United Kingdom at the end of the period of the visit as stated by him; and does not intend to live for extended periods in the United Kingdom through frequent or successive visits; and
will remain in place. Granted that this places a lot of discretion in the Immigration Officer's hands, but more importantly those who are not abusing their visits have nothing to worry about. The rule is targeted at people who basically try to live in the UK without the proper visa and people who use the UK to reset their Schengen clock.
Paragraph 23A of the rules, which allows US citizens (and others) to obtain 'leave to enter' upon arrival will not change.
A person who is not a visa national and who is seeking leave to enter on arrival in the United Kingdom for a period not exceeding 6 months for a purpose for which prior entry clearance is not required under these Rules may be granted such leave, for a period not exceeding 6 months.
In summary, the answer to your question is: you will still be able to obtain 'leave to enter' with your passport and you are NOT obliged to remain outside the UK for a specified interval between visits.
UPDATE: Paragraph 41 referred to above was replaced by Appendix V 4.2 in 2015:
will not live in the UK for extended periods through frequent or successive visits, or make the UK their main home