Chalfont's letter comes as the Ministry of Defence finalises its formal response to a Lords Select Committee report published in January. In an historic finding, the committee concluded that two RAF air marshals were "not justified" in finding that the pilots of Chinook ZD576, which crashed on the Mull of Kintyre in June 1994, were negligent.
The Lords report said there was doubt over the cause of the crash because of the possibility of a technical malfunction, such as the pilots' controls jamming or a sudden engine surge caused by the Chinook's safety-critical Full Authority Digital Engine Control software.
"Any of these events could have had a serious effect upon the crew's ability to control the aircraft," said the report.
Now Chalfont, head of the Mull of Kintyre group of peers and MPs, has asked Tony Blair to take independent advice on the committee's report.
Chalfont's letter asked the prime minister to "give your personal attention" to the crash of the Chinook helicopter ZD576. He added, "I am aware that this matter lies within the responsibility of the secretary of state for defence and that normally you would pass the matter for him to deal with. However, I earnestly beg you to have the matter, including the House of Lords Select Committee report, looked at by someone outside the Ministry of Defence, as the air staff, who have been dealing with it throughout, will simply provide the brief which they have adhered to for years. The issue has now reached a critical stage."
Chalfont told Blair that the MoD was unlikely to act on the Select Committee's conclusion by overturning the verdict. Should this be the case, the campaign of the Mull of Kintyre group may be stepped up. For example, MPs and peers may begin to raise the constitutional matter of whether the final say over what or who caused the crash should lie with officials or Parliament.
"All this can be avoided if the Ministry of Defence will accept the finding of the House of Lords Select Committee and set aside the verdict of gross negligence against the Chinook pilots," said Chalfont in his letter.
"This is a matter, prime minister, of natural justice which should not be left to a governmental department in which officials might justifiably be suspected of a conflict of interest. I beg of you to intervene before the secretary of state for defence signs off his response to the House of Lords Select Committee, and opens up issues which will go far wider than the responsibilities of one government department."