Officers working for the British Transport Police (BTP) have been given Tasers in response to the heightened terrorism threat.

However, Liberal Democrat MSP Liam McArthur criticised the "rushed" plan, while Amnesty International also expressed concerns.

In September, the force announced that a number of specially-trained officers based in Scotland would soon have the capability to use Taser devices.

BTP officers in other parts of the UK carry the so-called stun guns, but colleagues north of the border have not had the same power until now.

A letter from BTP Chief Superintendent John McBride to McArthur revealed Tasers would be deployed from yesterday onwards:

“The training of BTP officers has gone well and to plan. We have secured sufficient volunteers to undertake the national accredited course for specially trained TASER officers and have had a good pass rate.

“This has put us in a position where we can now go live with those deployments. The first officers will deploy with the devices on Thursday 13 October.”

The force has not confirmed, for "operational reasons", the number of officers who will be carrying the devices, but said Tasers would be deployed where officers needed to protect the public or themselves.

In December last year, police used a Taser against a man in east London, who was armed with a large bladed knife and who had targeted a stranger. Each deployment will be recorded and reviewed.

Arming officers with the high-voltage devices followed discussions with Police Scotland and Scottish Ministers were briefed on last month's decision.

McArthur said: "Police officers need to have the tools to keep us safe but the way this announcement was rushed out at the last minute will raise eyebrows. This is a major change and it needed to be scrutinised properly.

“Instead we find that tasers are to appear on our railways a matter of hours after this is confirmed by BTP. We still have no idea where they will be deployed or on which routes. This is not the way to build public confidence."

Naomi McAuliffe, Amnesty International's Scotland Programme Director, said: "Although we are concerned about police officers carrying potentially lethal weapons in our rail stations, it is encouraging that British Transport Police have pledged these officers will receive rigorous training and will only use the Taser device if they feel there is a serious threat to their personal safety or the public.

"However, we would like to see clearer guidelines for use and expect robust monitoring of any Taser deployment in Scotland's transport network as well as transparency about the circumstances of any incidents."

Control of railway policing was devolved to Holyrood, under the latest tranche of powers to be transferred from Westminster.

The Scottish Government wants BTP to be integrated with Police Scotland, but Opposition politicians are against the plan.

A spokesperson for BTP said: "Each of the officers has been through a rigorous training programme, which will be refreshed on a regular basis. They will only be using the equipment if they feel there is a serious threat to the safety of themselves or a member of the public"