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Hello, I hope you are well. My name is***** am a solicitor advocate and I will be assisting you with your question today. I am very sorry to hear of the problem you are experiencing and I will do my best to help you with this matter.
As a tourist from the USA you are allowed to enter and stay in the UK for up to six months with out a visa.
That is, six months in total in any 12 month period. If you have visited the UK more than once and stayed longer than 6 months in a 12 month period, then you were lucky to have done so without being stopped on entry.
It really is a matter of luck, if you are stopped and refused entry if you come for Christmas and have already stayed in the UK for 6 mouths in total in the last 12 month period.
If you can show proof of you job, studies and retune ticket, then luck may be on your side and you could well get in again.
Sorry I mi read the question and it somehow got muddle with another.
You are of course correct that there is no written rule about 6 months max for US tourists.
You can indeed come and go as often as you wish and stay for up to 6 months son any one visit.
The only risk you may have at boarder control would be if you have been spending a lot of time in the UK and very little time out of the UK. The boarder control could see this as a simple attempt to bypass immigration and visa requirement and to stay semi permanent in the UK. If you are stopped and they suggest this, you would need to convince them that is not the case. The should be fairly easy to do as you were stuck in the UK because of cover, so that was out side your control, you can show a return ticket and proof of job in the USA.
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