Avanti West Coast should be stripped of its contract unless axed services are reinstated soon, Greater Manchester mayor Andy Burnham said.
The Labour mayor wrote to Transport Secretary Anne-Marie Trevelyan warning that the company’s existing plans for increasing its timetable will cause “two more months of chaos”.
The operator reduced its timetable from seven trains per hour to just four per hour on August 14.
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This involved running just an hourly service in each direction between Manchester and London, compared with three per hour previously.
The changes were made to cut short-notice cancellations after a sharp decline in the number of drivers voluntarily working on rest days for extra pay.
Avanti West Coast’s contract from the Government to run services on the West Coast Main Line is up for renewal at the end of next week.
Last month the company published a plan to reinstate some services on certain days from September 27.
Timetables on other days were due to be boosted “as soon as possible” ahead of another increase on December 11.
In his letter, Mr Burnham wrote: “This would mean two more months of chaos on the West Coast Main Line in the interim, with resulting damage to our city-region’s economy.
“If 11 December is to be acceptable, Avanti must also commit to providing a consistent two trains per hour service between Manchester and London by the end of this month, as a staging post to full restoration of the timetable.
“Unless this happens and is clearly communicated, train travel between our most important economic regions will continue to be chaotic, forcing people into their cars or into abandoning plans to travel entirely.
“Without this commitment, I will be unable to support a new contract for Avanti.”
Mr Burnham told Ms Trevelyan that Avanti West Coast still has “very poor levels of reliability”, with trains “regularly delayed or cancelled”.
His letter mentioned “other challenges” including tickets only being released a few days in advance, seats being double booked and broken toilets.
“These dreadful conditions would be unacceptable at any time but are particularly so now given the wholesale collapse of the timetable, something no other train company is experiencing at anything like this scale,” Mr Burnham wrote.
Avanti West Coast said in a statement: “Our revised timetable has reduced the percentage of short-notice cancellations and so improved reliability for our customers.
“We’ve also worked hard to produce a plan to incrementally increase services, particularly on the Manchester route which is our busiest, over the next two months, and then in December we are planning to return to a full timetable on most of our network.
“Nevertheless, we know that at the moment we’re not delivering the service our customers rightly expect and we apologise for the enormous frustration and inconvenience this is causing.
“We would like to thank our customers for their patience and understanding.”