I can't guarantee that it will happen automatically, so I think it would be wise to contact Admissions to ask whether the invigilation report for both tests will be available at the hearing, as it will be an important part of your case. (Best to do this in writing so that there's a record of your inquiry. Email: email@example.com
, quoting your appeals reference number, name of child, date of birth, & name of school.)
I must warn you that, because of the Data Protection Act, it's likely they will have to blot out the name of any other child.
Would it be possible to get a letter from the school confirming where your son was sitting and that it was next to the child who was ill? (I'm assuming the test was at your son's own school.)
As Herman says, the difficult bit is proving what effect this would have had on your son. It would have helped if you had medical evidence about your son's near phobia, and of any other situations where this has been a problem.
I'm afraid lots of children have unexpected scores in the 11+.
The academic evidence is usually even more important than extenuating circumstances. A really good verbal comprehension score from the EP (90th percentile or higher) would help.