The Dalzell plate mill in Motherwell was mothballed by Tata Steel in 2015, with the loss of 225 jobs, before being taken over by Liberty House Group in April.

Liberty has spent the last five months rebuilding the workforce and recommissioning equipment at the huge site, which includes the UK’s largest and most versatile plate mill.

Dalzell is the last major steelworks in Scotland and, over several generations, has provided Britain with the tough steel plate used in industries such as shipbuilding, construction, mining, oil production and heavy vehicle manufacture.

Speaking ahead of the event the First Minister described its revival as “a very positive signal that the steel and engineering industries still have a future here in Scotland”.

Sanjeev Gupta, executive chairman of Liberty House, described the re-opening as a first step for the group in Scotland, adding that he aims to expand his company’s investment there in pursuit of its Greensteel strategy for a competitive, low-carbon and sustainable steel industry.

Liberty has already recruited around 120 staff for Dalzell, comprising many former employees who have returned, as well as those new to the industry including several apprentices who have begun training for a variety of jobs. It is hoped employment will increase to over 200 within 18 months, as production rises in response to market demand.

The reopened plant will be targeting Britain’s 700,000 tonne-a-year market for plate steel which is estimated to be growing at the rate of 3 per cent a year. The business has already secured a significant number of orders for plate that will be used particularly in the construction and energy sectors.

In the medium to longer term, the plant, which has a full production capacity of between 400k and 500k tonnes a year, is expected to not only re-establish its previously-held position in British markets but to develop new routes to market and secure new customers across the UK and abroad.

At a local level it is estimated that the restart of Dalzell will be worth roughly £15 million a year to the economy around Motherwell, both in wages and supply contracts awarded to local businesses.

First Minister Nicola Sturgeon said: “This is a fantastic day for Dalzell workers, for Motherwell and for Scotland’s steel industry. Restarting steel production has only been possible thanks to the tremendous team effort of everyone involved in the steel taskforce to find a viable future for this site, meaning workers here in Lanarkshire can once again produce world-class products.

“Liberty House are seizing an exciting opportunity and the Scottish Government and its agencies will continue to work with Sanjeev Gupta and his team to ensure a successful future in Scotland.”

Executive chairman of the Liberty House Group, Sanjeev Gupta paid tribute to the support of the Scottish Government and Scottish Enterprise in helping the company rescue the plate works.

He said: “There is an impressive spirit of partnership here and a determination to give the Scottish steel industry a real future. From our side we promised we would get this important plant open again by the autumn and today we are proud to be fulfilling that promise.”

He disclosed that the neighbouring Clydebridge works at Cambuslang would come back on stream in due course as market conditions allowed.

Mr Gupta added: “We see great opportunities for investment in Scotland and regard this as a very fertile business environment in which to deliver our Greensteel vision.”

Jon Bolton, chief executive of Liberty Steel UK Plates & UK Steel Development, said: “Restarting this mill only nine months after production was halted has been a tremendous achievement. Seeing the plant producing steel plate once again is just reward for all the determination and hard work of the team here at Dalzell. We now intend to ramp production up as quickly as the market will allow.”