Blunkett was not allowed inside the venue because he had his guide dog with him.
According to The Telegraph, the letter said: "We pointed out immediately that this was the Paralympics and that my name was on one of the seats, with the clear understanding that it was likely that I would have brought my dog.
"I chose not to have a hissy fit. I felt that this was not an occasion to make an issue of the occurrence, not least because we were in the proximity of the broadcast media operation.
"We were allocated moveable seats on the gantry which whilst sufficing was clearly nowhere near as satisfactory as sitting in the stadium for a variety of reasons, not least the way they were exposed."
Great Britain have won 20 medals in the opening two days of action.