Former Ukip leader Nigel Farage is set to meet the EU's Brexit negotiator Michel Barnier to represent "the views of the 17.4 million".
Mr Farage has called on people to tweet questions with the hashtag AskBarnier ahead of Monday's meeting in Brussels.
The anti-Brexit pressure group Open Britain derided the decision, saying it was "like sending an arsonist to put out a house fire".
Speaking in a Twitter video, Mr Farage said: "Who is in there representing the views of the 17.4 million? Nobody.
"Well I've finally got my meeting with Mr Barnier, it's going to happen 11am next Monday morning in Brussels, but I want to involve you.
"I want you to ask your questions directly to Michel Barnier, so respond, give me your name, give me your home town, give me one question use the hashtag AskBarnier and I'll pick the best three."
James McGrory, executive director of Open Britain, said: "Sending Nigel Farage to Brussels to sort out Brexit is like sending an arsonist to put out a house fire.
"After years of poisoning our politics, telling outright lies about the EU and cosying up to Trump, he has already done enough damage to our country and our international standing.
"He has no answers to the costs and complexity of Brexit, other than to blithely say we should walk away with no deal, which would be an unmitigated disaster for our economy and our country."