The gift, in 1997 before the May election, triggered a storm of controversy when it was alleged the money influenced the government's later decision to seek an exemption for Formula One from a European tobacco advertising ban.
The Conservatives demanded a fresh look at the affair, which first surfaced almost three years ago, after claims in a new book by journalist Andrew Rawnsley.
It said Prime Minister Tony Blair and Chancellor Gordon Brown lied about the pre-election donation, which Labour later returned on the advice of Lord Neill.
The gift, in 1997 before the May election, triggered a storm of controversy when it was alleged the money influenced the government's later decision to seek an exemption for Formula One from a European tobacco advertising ban.
Conservative frontbencher Andrew Lansley wrote to Lord Neill in September asking him to reconsider his earlier advice and whether Mr Brown and Mr Blair had misled him.
He voiced concerns that a 1997 letter to Lord Neill from then Labour general secretary Tom Sawyer was written to distract media attention from the episode.
But Lord Neill, chairman of the Committee on Standards in Public Life, rejected the call in his reply on Wednesday.
"The then prime minister, John Major, made it clear when he announced the establishment of the committee in 1994 that our remit does not extend to investigating individual allegations of misconduct," Lord Neill said.
"In this exceptional case, before we began our enquiry into the funding of political parties, and indeed before we had received the precise terms of our remit for that study, I gave advice to the Labour Party on a matter which required a speedy response.
"In order to ensure that the public had access to the correct information, I made my letter publicly available at the time.
"I believe that openness is an important safeguard in such circumstances, enabling the public to judge for themselves."
Mr Rawnsley's book alleged that Gordon Brown told BBC Radio 4's Today programme he knew nothing about the donation, but admitted privately afterwards that he had lied, saying: "If this gets out, I'll be destroyed."
The book also makes claims surrounding the advice Mr Blair sought from Lord Neill, it had been thought before any journalists had been in touch.
Mr Rawnsley says in fact the prime minister contacted Lord Neill only after reporters began to break the scandal.
And his letter asked for advice about a second offered donation, not the first, according to the book.
But Mr Blair later dismissed the allegations as re-hashed "old stuff".
Insisting he had acted properly over the affair, the prime minister said: "We decided to ask the standards watchdog whether we should repay the money and what we should do in these circumstances where there was an apparent conflict of interest even though nobody had ever asked us to do anything improper.
"With the published correspondence at the time you can see we mentioned the first donation too. We did ask for guidance on it."
A spokesman for Mr Brown said the book told the country "absolutely nothing" about what had happened.