Theresa May will vow never to allow the UK to become "looser and weaker'' in a speech ahead of a meeting in Scotland with Nicola Sturgeon.
Day Of Protests In Campaign For Safer Railways
The RMT union is staging a day of protests in support of its Safer Scottish Railways campaign.
The move follows calls by the transport workers' union for the Scottish Government to set out an immediate timetable for Abellio to be stripped of its ScotRail franchise.
RMT claims performance by the under-fire operator has slumped and not enough money is being invested in staffing, services and safety.
ScotRail said the comments did not stand up to scrutiny and added that it was investing hundreds of millions of pounds on new trains and systems.
RMT members will be campaigning at stations in Dundee, Dunfermline, Glasgow, Edinburgh, Inverkeithing, Kirkcaldy, Motherwell, Stirling and Tweedbank, urging members of the public to sign up to the campaign through postcards to politicians.
Almost 20,000 people have already signed a petition calling on Transport Minister Humza Yousaf to ''make ScotRail bosses improve Scotland's trains or strip them of their contract''.
ScotRail was recently fined £483,000 for failing to meet required standards for trains and stations.
First Minister Nicola Sturgeon last week indicated that stripping ScotRail of its contract to run the railways was on the table if performance failed to improve.
RMT general secretary Mick Cash said: "RMT is campaigning to make Scotland's trains safer, more secure and accessible.
"This can only be done with a publicly owned service where profit isn't the main motive of the operator.
"RMT calls on the Scottish Government to set out a timetable for bringing ScotRail under public ownership and, with the current level of anger that's reinforced in the petition, there can be no excuse for the dragging of heels.
"The union is available for talks with ministers to take the issues of safe staffing, investment and public ownership forwards.''
A ScotRail spokesman said: "These comments bear no scrutiny whatsoever. Performance has dipped by around 1% - but is still tracking around the 90% mark - and we have a robust performance improvement plan to rectify that.
"At the same time, we are investing hundreds of millions of pounds on new trains, refurbishing our existing fleet and introducing queue-busting smart technology to keep people moving.''
Dutch company Abellio was awarded the franchise in 2015 for 10 years but ministers can strip the company of the contract after five years if punctuality falls below 84.3%.
Charlotte Twyning, director of policy, strategy and communications for Abellio, said: "We are committed to the ScotRail franchise and to delivering for Scotland. The RMT is completely wrong to state that money is being taken out of Scotland - on the contrary, we have invested in a headquarters in Glasgow and a customer service centre in Fort William, creating and maintaining jobs.
"Under the Abellio franchise, ScotRail is a living wage employer. The truth is our people are working hard - with the Scottish Government and Transport Scotland - to improve customer service during a sustained and significant period of railway modernisation and this kind of statement does nothing at all to help passengers or staff.''
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