Type of   check and cost        What it will check for                                                                                   How long it normally takes
Standard -      £26                Spent and unspent convictions, cautions, reprimands, final warnings   About 2 weeks
Enhanced -    £44                As above - plus information from local police records                           About 4 weeks
Checks for volunteers are usually free of charge.  
best to go through the crb agency themselves , and you will need several documents from your employees 
or experian do a crb check as but costs more