Crony Gets Peerage - Is this Government Corrupt?
Mr Johnson defended his nomination of Mr Cruddas in a letter to Appointments Commission chairman Lord Bew.
The Prime Minister rejected "historic concerns" raised about Mr Cruddas, relating to allegations that he offered access to then-prime minister David Cameron in exchange for donations.
Mr Johnson said: "The most serious accusations levelled at the time were found to be untrue and libellous," and an internal Conservative Party investigation "found there had been no intentional wrongdoing".