Housing Benefit rates - list of rates and rises? Tenant paying full amount?

Housing Benefit Overpayment

Hi, Im a relatively new LL and have made a few classic awful mistakes, NRLA helping me sort them out.  You will see a lot of me here over the next few weeks :-) 

Is there any way to check what LHA rates have been over the last decade, from 2015?  Is there any way the tenant could have been paying me part of the LHA and pocketing some for himself?  

My tenant was sitting when I purchased, I took him at face value and did not do any credit checks or references or guarantors.  He is on State Pension and full Council Housing Allowance.  Our current AST is an incomplete mishmash supplied by him on premise of LHA rises, and pressured into signing because he had to provide evidence to the Council that I had signed.  However no verification from the Council to me.  Is this right?

PS I know I've made some gross errors :-((, believe me Im trying to sort it out now