Is a sponsorship letter required for obtaining UK transit visa for Indians? [closed]

I am travelling to schengen countries next month, and for one of my flights I need a transit visa for the UK, as the flight lays over in London for 10 hours.

So my query is, whether I will need a sponsorship letter attached with visa documents as my wife is travelling with me and in the application form I have shown that I am sponsoring her for the visit.

My confusion is that in the transit visa documents nothing is mentioned about the sponsorship letter.