Been having a bit of a dig around the electoral commissions website and found this 
http://www.electoralcommission.org.u...ampaigners.pdf
This bit is quite interesting 
	Quote:
	
	
		
			
				What is referendum 
spending? 
Referendum spending is expenditure on certain campaigning 
activities (listed on page 6) that are intended to, or are 
otherwise in connection with, promoting or bringing about a 
particular outcome in the referendum. 
It includes spending on: 
 items or services used during the referendum period 
including those bought before the period begins 
 items or services used during the referendum but paid for 
after it 
 items or services given to you free of charge or at a noncommercial 
discount of more than 10% (see ‘Notional 
spending’ on page 11 and 12)
			
		 | 
	
	
 I don't know if i'm reading this correctly but it appears that Cameron has breached the rules