"long-standing colleagues" is a correct and usable phrase in written English.
You can use it when referring to colleagues who have worked together for a long period of time. For example, "Sam and I are long-standing colleagues, having worked together for more than 10 years."
The language Mr Livingstone used to disparage a long-standing colleague, no matter what the provocation, belonged in another age.
The Association of the Attending Staff of the Mount Sinai Hospital mourns the passing of our long-standing colleague, teacher, and friend.
The Association of the Attending Staff of the Mount Sinai Hospital mourns the passing of a long-standing colleague, teacher and friend.
LAPID--Louis S. The Association of the Attending Staff of the Mount Sinai Hospital mourns the passing of our long-standing colleague, mentor and friend.
Terry will not have his long-standing colleague Ferdinand alongside him after the Manchester United was omitted due to doubts over his fitness.
$6$$)GLABMAN--SHELDON, MD The Association of the Attending Staff of the Mount Sinai Hospital deeply mourns the passing of our long-standing colleague, mentor, and friend.
KUHN--Leslie A. The Association of the Attending Staff of the Mount Sinai Hospital mourns the passing of our long-standing colleague, teacher and friend.
He intends to keep the management fees for the fund at 1% – which he says is lower than the industry norm – and he will manage it in London, with long-standing colleague Julian Robins based in Connecticut, in the US.
After his long-standing colleague Andy Gray was fired by the broadcaster on Monday for "unacceptable behaviour", Keys's position had appeared untenable since the emergence of new evidence of his own sexist behaviour later the same night.
But his parting shot at the party leadership has also ricocheted off his long-standing colleague Mr Cable.
This, after all, was the Scottish architect's masterpiece – designed with his long-standing colleague Isi Metzstein – and, though the erudite and entertaining pair had built many new modern Roman Catholic churches, St Peter's seminary was very special indeed.
