Neil,
As a Health & Safety manager for a large group of companies I would just ask the site management for a copy of their up to date fire safety risk assesssment as required by law under the Regulatorary Reform (fire safety) Order 2005 & then look for the risk asseessment that states that it OK to place caravans so close together! then I would ask him why he chooses not to comply with the accepted code of practice (re the CC) regarding spaces between caravans.
The site owner has a legal responsibility under the above act, sections, 4 (1) (a) to reduce the risk, under 8 (1) (b) the safety of persons who are not employees, under 9 (1) make a "suitable & sufficient risk assessment & finally under 22 (1) share that information
Take a look at www.opsi.gov.uk/si/si2005.htm for the full details.
The owner of the site cannot under law refuse you this information & if he does I would suggest a quiet word with the local fire authority.