Ukip thinks it is entitled to 23 more peers to make the Lords better reflect the share of the vote in the last general election.
The party has issued fresh demands for greater representation in parliament as it seeks a stronger foothold.
Former Ukip leader Lord Pearson of Rannoch has written to the Cabinet Office to ask for more members of Nigel Farage's party to join him on the House of Lords' red benches.
He said it was "transparently dishonest" for the party not to have a greater representation in the upper chamber than the three current members, who all defected from the Tories.
The party believes it is entitled to 23 more peers under the Government's ambition of making the composition of the Lords better reflect the share of the vote gained by parties in the last general election in 2010.
In a letter to Cabinet Office Minister Francis Maude, seen by the BBC, Lord Pearson said the Government's failure to appoint Ukip members represented the "sort of behaviour which makes the political class so increasingly unpopular with real people".
He said the case for more peers was "even stronger that it was before" following Ukip's success in the European elections, which saw the party top the polls with 27.5% of the vote.
Lord Pearson told BBC Radio 4's Today: "Our democracy requires that we have more than three peers in the House of Lords when we're getting 27% of the vote in the latest national election. I mean it is transparently dishonest.
"It is dishonest for over a period of four years to go on saying we're going to do this and then making it perfectly clear that we've no intention of it."
The coalition agreement, setting out the basis for Ukip's claim, states that "Lords appointments will be made with the objective of creating a second chamber that is reflective of the share of the vote secured by the political parties in the last general election".
The letter is the latest attempt by Lord Pearson to persuade ministers of the need for action.
In March last year Lord Pearson wrote to Mr Cameron suggesting "half a dozen" extra peers as a compromise and then in a handwritten addition pleaded for "some, anyway?."
A reply signed by a Downing Street correspondence officer told him the letter was "under consideration."
Following May 2013's local elections, Lord Pearson wrote again and in a handwritten amendment added "they would support the Government, most of the time" - although he told Today that would no longer apply.Suggest a correction