taking the forgery bit out of the equation, if he has not been paying suppliers,tax, paye,vat etc. you are still liable for the FULL amount, all partners are equaly liable for all the debts, regardless of who should of done what,and as hymie says HMRC dont take no c**p they will take the easiest option to recover there money and as the other guy has gone bankrupt that leaves you !! They are not interested in excuses or partnership squabbles.
Been there myself , cost me �1,000s ,partnerships are a minefield unless set up properly at the beginning, unfortunately most are formed between so called mates who trust each other...