The Conservative Friends of the Union (CFU) group is charging £750 a head for the event.
Although the Scottish Tories are part of the pro-Union Better Together campaign, CFU is the party's internal group opposing independence.The Edinburgh-based body reportedly has a six-figure war chest and will hold fundraising events.
However, CFU's Scottish credentials were questioned in March after it was revealed its first dinner was run by the English-based "United and Cecil club" from a house in Sussex.
The event, held Edinburgh, included Conservatives bussed in from south of the Border.
A leaked circular flagging up the next CFU dinner has opened the door to more criticism.
Written by party treasurer James Stewart, the event, "in support of Scotland remaining within the United Kingdom", is to be held at the "majestic" Crosby Hall mansion in Chelsea, a "historic mediaeval building".
Speakers include Surrey Heath MP Michael Gove and hereditary peer Lord Strathclyde.
A senior Conservative source said: "This is yet another own-goal and more ammunition for the Nationalists. Everything is done through a London prism."
An SNP spokesman said: "This confirms that the No campaign is Tory-led and is being funded and driven from south of the Border."
A spokesman for the Scottish Conservatives said: "The Sunday Herald must be struggling for stories if it thinks a political party holding a fundraising dinner for its supporters ahead of such a crucial decision is newsworthy."
BY PAUL HUTCHEON