Guido 
  i have just sorted this minefield out over the last few months! 
 fact 1
 it is not a legal requirment, unlike Employers liability 
 (WHICH IS) 
 secondly you need it if you are not a limited co! 
 The reason is if you  are to be acused of being negligent  
 you could be sued , and loose your house etc etc  
 if you are limited different rules apply1  
 now the clever bit! your premium will be  in-line with the category you ask to be in ! 
 ie my  holiday trips were put in (travel agents) cost over £13000 public liability for 5.000.000 cover 
 noew i'm in (events organiser) £976.00 for 2.000.000 cover 
 make sure you dont get ripped off !!!!! do your homework
 
  hope this helps mate ,,,,,,,,,,,,,,,,,mav