The writer Ian McEwan has received an apology from the US government after he was refused entry to the country the day before he was to deliver a lecture to 2,500 people in Seattle.

The author, a favourite of the first lady, Laura Bush, was stopped last month by US immigration officials as he left Vancouver airport in Canada. In what has been described as a very "unusual" move, the writer was sent a letter saying: "Please accept my apologies for any inconvenience and delay the refusal caused you. Be assured that this erroneous refusal will not impact your future applications to the United States."

McEwan has been told to keep the letter inside his passport - which now bears a stamp advising that he has been refused entry to the US. The letter is "a means of clarification and facilitation at a US port of entry".

The author, who last year was invited to Downing Street by Cherie Blair to meet Mrs Bush (known to keep a McEwan novel by her bed) eventually gained entry to the country after much diplomatic scuttling. He made it to his lecture with just an hour to spare.

McEwan, who recently won the US National Book award for his novel Atonement, said: "It is gratifying to have an apology. I was fortunate, but I understand there are other artists and performers who have had similar problems and were turned away. It's a great shame that the US should reinforce its isolation - since it needs all the friends it can get."