Is a sponsor letter required to obtain a UK transit visa for INDIANS?

Hello, I am going to the Schengen countries next month and for one of my flights I have to take the Transit VISA from UK as the flight is 10 hours in London.

So my question is, will I need a sponsored letter with a visa, as my wife travels with me and has shown in the form of an application that I sponsor her for the visit.

Confusion is that the transit visa does not mention anything about the sponsorship letter.

So thoughts are valued equally.