Keir Starmer is expected to name around 30 new peers on Thursday – with a gong for former aide Sue Gray.
The Prime Minister will nominate dozens of people for peerages in a bid to swell Labour‘s numbers in the House of Lords.
Labour has promised to slim down the House of Lords, with a bill to abolish hereditary peers currently going through Parliament.
Tony Blair slashed numbers of those who inherited their titles but 92 remained as a compromise.
Despite commitment to reform the Lords, the Government is concerned about getting legislation through the upper chamber.
There are currently 273 Tories, 187 Labour, 78 Lib Dems and 184 cross-benchers, meaning no party has a majority.
Ms Gray, who hit the headlines when she led a probe into Partygate, quit as the PM’s chief of staff in October after a slew of internal rows.
She is expected to be among a string of appointments of Labour figures, which are believed to outnumber the Tory peerages that will also be announced.
Tom Brake, Director of Unlock Democracy, said Labour needed to stick to its commitment not to pack out the Lords.
He said: “We hope at least that all new peers will be committed to wholesale reform of the Lords. This would provide some consolation for their swelling numbers.
“Although new appointees to the Lords will now have to be ‘justified’, this falls far short of Labour’s pre-election pledges.
“At the very least, the government must rapidly deliver on its manifesto promise of a proper consultation on the future of the Lords.”