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I normally check everything, we went to France on holiday in the motorhome no problem going, coming back, going through customs etc they asked for passports (going you just waved your passport at them) handed them over, they asked for mine, I said you have it, they said we have 2 bearded mens passports, I looked at them one was OH the other was my brothers. The previous Christmas we had rented a cottage in France and all the family came, how the heck I had brothers passport instead of mine I do not know. They didn't want to let me back in the country saying I hadn't left, I was panicking, it took nearly 2 hours before they would let me into GB.
I learnt my lesson, I double check everything now.