Police described it as "terrifying''.
MSPs To Hear British Transport Police Merger Plan Concerns
The Chief Constable of the British Transport Police (BTP) will outline concerns to MSPs about plans to merge the force north of the border with Police Scotland.
Paul Crowther will be questioned by members of Holyrood's Justice Committee about the issue, along with Police Scotland Assistant Chief Constable Bernard Higgins.
Ministers at Holyrood have put forward legislation that, if passed, would give power over railway policing to the force and the Scottish Police Authority (SPA) watchdog.
The BTP fears the proposal, in the Railway Policing (Scotland) Bill, could see the loss of its "specialist approach'' which provides "seamless'' coverage across the UK's railways.
In a written submission to MSPs, transport police said the current system "avoids the need for officers to disembark'' when travelling across the border between Scotland and England
This protects the travelling public and also prevents disruption to operators of cross-border services, including "the regular policing of football supporters travelling between cities and towns in Scotland in to the north of England and vice versa''.
The force also stated: "Specialist train services including nuclear trains, MoD trains and the Royal Train are also currently policed in a continuous manner by BTP operations that consider the implications of the end-to-end route.
"Introducing new arrangements that necessitate the handing-over of command for any of these services will need to be carefully developed.''
Police Scotland said the lessons learned from its own creation - when eight regional police forces were brought together to create a national body - would be applied to the integration of BTP.
The force said: "It should also be noted that during the early life of Police Scotland a highly professional level of service continued to be provided to the communities of Scotland.
"During the integration of BTP we will aim to ensure this is replicated across Police Scotland and the railway network.''
Police Scotland's submission highlighted its intention to "retain the current specialist skills and knowledge built up by BTP officers to ensure a smooth transition into Police Scotland'', adding a training programme would be developed to "upskill'' current frontline Police Scotland officers.
The force insisted: "Devolution of railway policing will have no detrimental impact on cross-border security arrangements.
"BTP and Police Scotland currently work together on a number of cross-border operations and this close working relationship would be expected to continue with BTP colleagues south of the border, following April 1 2019.''
A Scottish Government spokesman said: "As Police Scotland have made clear, specialist railway policing expertise and capacity will be maintained and protected within the broader structure of Police Scotland, with improved access to wider support facilities and specialist equipment, providing an enhanced service provision to the rail industry and travelling public.
"Devolution of BTP's functions was recommended by the Smith Commission, reached through cross-party agreement and integration will also ensure railway policing is fully accountable to the Scottish Parliament.''
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