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I was recently issued with a U.K. Standard visitor's visa. It's valid for 6 months and multi-entry. When I applied, my intended travel dates were in December. However with new family developments I am unable to travel in December. My purpose for traveling to the U.K. hasn't changed, nor has the duration, the only thing that has changed is the date. Would I have problems entering the U.K on a changed date that is still within my visa validity?