Peedal it sounds like we had the exact same thing happen to us a few weeks ago
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Fiancee and her son came to the UK, to try the country (and living with me lol) on for size so to speak. They fully intended to head back to the United States to apply for the correct visas in the proper manner. Of course convincing the IO's at Heathrow TN4 of that proved a much more difficult proposition. On reflection we can understand why there suspicions were aroused, but their point blank refusal to listen to our logical and totally honest explanations, and their instance that their ASSUMPTION of our wishes to live illegally must be correct, will rankle for a very long time.
For the record, our plans and situation that caused the 'issues' were:
1- No return ticket. We reasoned that because it was a long summer we would take our time, and try to time the return to the states to coincide with having all the visa applications completed and ready to apply. All we wanted to do was maximise our time together, and minimise the time spent apart, but it meant we didnt have an exact return date.
Doh! This was the question that tripped the whole thing off.2- A lot of luggage. We used up the full allowance of luggage on the plane. No more than allowed, but on the limit. To the IO's this was too much for a visit. We were bringing things over in advance of the final move later in the summer, to get around flight baggage restrictions. Did they believe us? Nope.
Still difficult to accept this, if there is a recommended amount of luggage that immigration officers accept as suitable for a visit then it might be useful if they told us.3- Fiancee's cirmcumstances meant she had no reason to return to the US. After the detention interview, they decided that my Fiancee's life in the US must be so bad that she would have no reason to return. Why? Because she had moved in with her sister prior to coming over (had no permanant address of her own you see) and was between jobs.
This is the killer for us. It just seems to smack of attempting to justify their decision after the fact. The simple assumption was that living in the US legally with her friends and family for a few weeks, whilst applying for a settlement visa, was somehow less preferable than living with an illegal status in the UK.End result? 2 days temporary stay in the UK with fiance (and yeah, if they were going to then they could have run off) before having to head back stateside. Still we got a free flight courtesy of the UK Government, which saved us a bit of money. Not that this in anway offsets or compensates the sheer distress and discomfort caused by spending 10 hours in detention with a young child. Grrr it really makes the blood boil.
Sorry if this worries anyone, I would lay odds that we probably just ran into the wrong IO on the wrong day, but still take heed. It was the return tickets issue that kicked it all off, everything else just seemed to be justification of the decision to refuse entry rather than a decent reason in itself.
Anyway, just like Peedal, all that has happened is that we have pulled our plans forward by a month or so, and are very nearly ready to send in the applications. Fingers crossed then we can get it all behind us and look forward to our wedding in September. Pretty sure we wont be using Heathrow to fly back in though...