Mr Allan said: “The positive result from the test was delivered at 8.03pm via text and email.
“She attended the SNP whip’s office and spoke to then chief whip Patrick Grady MP.
“She informed Mr Grady that she would be returning to Scotland tomorrow.”
Ferrier returned to the hotel at 9.20pm where she spent the night before returning to London Euston.
The hearing was told at the busiest time, the train was holding 153 passengers.
Contact tracers for NHS Test and Protect attempted to contact Ferrier on four occasions but were unable to do so, leaving two voicemails.
Ferrier later contacted Test and Protect and revealed that she had a “slight and infrequent cough” the day before the test.
Mr Allan added: “She said she didn’t think she would be positive.”
Ferrier then informed Grady and the Parliamentary Testing and Tracing Service that she was positive.
This led to Shannon being ordered to take a test and isolate himself in his hotel room, but he later tested negative.
Mr Grady was told the next day at a meeting in the Speaker’s office in the House of Commons that Ferrier’s actions had to be reported to the police.
“I deeply regret my actions”
Ferrier contacted the police and informed them of her breach before issuing a statement on social media.
She said: “Despite feeling well, I should have isolated myself while waiting for my test results and deeply regret my actions.
“I take full responsibility and encourage everyone not to make the same mistakes I have and to do everything they can to limit the spread of Covid-19.”
An initial investigation by the Metropolitan Police was handed over to Police Scotland.
Public health expert Dr Andrew Riley told police that Ferrier “significantly increased the risk of harm to both individual and public health.”
Ferrier surrendered to the police on 4 January 2020 where she was arrested.
Brian McConnachie QC, defending, reserved his plea in mitigation.
Sentence was adjourned pending background reports from Sheriff Principal Craig Turnbull until next month.
Despite calls from Nicola Sturgeon, who described the actions of her then MP as “dangerous and indefensible”, Ferrier has refused to give up the Rutherglen and Hamilton West seat, which she first won in 2015.
Ferrier could also face a recall petition if she is suspended from the House of Commons for 10 or more sitting days.
Whether a recall petition can be triggered will depend on the sentence Ferrier receives. A petition can be held if an MP is convicted of an offense and is sentenced to prison. The maximum sentence a Sheriff Court can impose is five years in prison.
If a signature campaign was launched, a by-election would be held if 10 percent of the voters in the constituency signed it.
A by-election would be closely contested between the SNP and Scottish Labour.
Ferrier came within 265 votes of losing the seat to Labor at the 2017 election, although she increased her majority to 5,230 in 2019.