The agency was called in early last week despite the fact that NTL retains Brunswick for its core financial work. M is the same agency Virgin Group used for this summer's successful NTL/Virgin Mobile merger.
The proposed deal with ITV has raised eyebrows - and initially some ridicule - in the City. But last weekend opinion became more favourable. The financial press moved from focusing on whether or not the deal would happen to speculation as to its size and the commercial logic involved.
NTL and Virgin Mobile last week revealed their new branding and name, Virgin Media, as a result of their £962m merger.
Virgin Group corporate affairs director Will Whitehorn brought in M to advise on the deal after NTL's initial £817m bid was rejected. It is thought the successful outcome prompted NTL to call in the City agency during early stage discussions with ITV.
So far, NTL has not confirmed it will table a bid for ITV, but it has confirmed it is in talks with the UK's most-established commercial broadcaster. The move is thought to have alerted Five owner RTL to step in with a potential bid.
NTL continues to retain Brunswick. ITV has worked with Citigate Dewe Rogerson for more than a decade.
M: Communications declined to comment.