Curiosity led me to look into this because there is no special arrangement for ESL children in Bucks, other than recourse to a Review or Appeal if they are unsuccessful in the 11+.
This is from the WCC Secondary School Admissions Guide for 2015 (link at the top of this page http://www.warwickshire.gov.uk/startingsecondaryschool
Will special consideration be given to children with certain learning or physical difficulties?
If your child has a learning difficulty or disability which could significantly affect their performance or ability to access the tests you must include detailed information with your registration form. This includes students with Statements of Special Educational Needs or those for whom provision is being made in a school at School Action or School Action Plus. It also includes those students where English is a second language.
Supporting information supplied must be dated within the last 18 months.
The Admissions Service will contact your child’s current school for confirmation of the information supplied. The Admissions Service will then consider the information provided and may seek further guidance in deciding whether to make specific adjustments for the candidate.
The Admissions Service will provide details of any provision or adjustments that are being made for a child before they sit the tests.
So, the answer is quite possibly "yes", and it's worth a phone call to establish what evidence might be required and what adjustments might be made. (I am assuming that the evidence would need to be utterly credible because otherwise this exception could be open to serious abuse.)
Please do report back for the benefit of others.