Oris Johnson’s leadership has been upset by growing calls from backbench MPs for him to step down.
The prime minister will face a vote of confidence if 54 Tory MPs write to Sir Graham Brady, chairman of the 1922 committee, demanding it be held.
If that threshold is reached, Tory MPs will vote on whether the Prime Minister should remain in office.
Half of Tory MPs are expected to vote against the Prime Minister for him to face a leadership race.
Eighteen Tory MPs have confirmed writing to Sir Graham so far, while 20 have publicly questioned Mr Johnson’s leadership.
More than half of the MPs who voted against the Prime Minister represent London, the South East or the South West.
Five London MPs – Sir Bob Neill (Bromley and Chislehurst), Stephen Hammond (Wimbledon), Elliot Colburn (Carshalton) David Simmonds (Ruislip, Northwood and Pinner) and Nickie Aiken, have so far called on Mr Johnson to stand down or hold a vote of confidence.
Tory MPs who said the Prime Minister should quit or publicly criticized him for partygate:
Elliot Colburn, MP for Carshalton (letter confirmed)
Stephen Hammond, MP for Wimbledon (letter confirmed)
Bob Neill, MP for Bromley & Chislehurst (letter confirmed)
David Simmonds, MP for Ruislip, Northwood and Pinner
Nickie Aiken, MP for the Cities of London and Westminster
Peter Aldous, MP for Waveney (letter confirmed)
Steve Brine, MP for Winchester and Chandler (letter confirmed)
Sir Roger Gale, MP for North Thanet (letter confirmed)
Caroline Nokes, MP for Romsey and Southampton North (letter confirmed)
Nick Gibb, MP for Bognor Regis and Littlehampton (letter confirmed)
Steve Baker, MP for Wycombe
John Baron, MP for Basildon and Billericay
Tim Loughton, MP for East Worthing and Shoreham
Angela Richardson, MP for Guildford
Dan Poulter, MP for Central Suffolk
Tom Tugendhat, MP for Tonbridge and Malling
Paul Holmes, MP for Eastleigh
Dame Andrea Leadsom, MP for South Northamptonshire
Gary Streeter, MP for South West Devon (letter confirmed)
Tobias Ellwood, MP for Bournemouth East (letter confirmed)
Mark Harper, MP for Forest of Dean (letter confirmed)
Anthony Mangnall, MP Totnes (letter confirmed)
Anne Marie Morris, MP for Newton Abbot (letter confirmed)
Aaron Bell, MP for Newcastle-under-Lyme (letter confirmed)
Alicia Kearns, MP for Rutland and Melton (letter confirmed)
Andrew Bridgen, MP for North West Leicestershire (letter confirmed)
Karen Bradley, MP for Staffordshire Moorlands
Nigel Mills, MP for Amber Valley
Andrew Mitchell, MP for Sutton Coldfield
Jeremy Wright, MP for Kenilworth and Southam
William Wragg, MP for Hazel Grove (letter confirmed)
Neil Hudson, MP for Penrith and The Border
Craig Whittaker, MP for Calder Valley
John Stevenson, MP for Carlisle (letter confirmed)
Robert Largan, MP for High Peak
David Davis, MP for Haltemprice and Howden
Andrew Jones, Harrogate and Knaresborough MP
Julian Sturdy, MP for York Outer