French transport firm Alstom could slash jobs in Britain after agreeing to buy Bombardier"s rail arm for $8.2bn (£6.3bn). The two companies have around 5,000 staff working on trains and the rail system in the UK - raising the spectre of cost cuts if the tie-up goes through. Alstom would likely look for savings that could lead to British plants being merged. Bombardier’s transportation arm has about 40,000 staff worldwide, around 10pc of them in the UK. Half the company"s British staff are at its train design and manufacturing base in Derby. Meanwhile about 2,000 of Alstom’s 36,000 staff are in Britain, spread across dozens of train service and maintenance depots. It also works in signalling and infrastructure. Steve Turner, assistant general secretary of union Unite, said: “Bombardier"s Derby factory is a first-class facility with a world-class workforce. “Unite has already received assurances from Bombardier that the sale of the company will not affect the Derby factory and its workers, and the union will now seek an urgent meeting with Alstom to receive similar guarantees.” Bombardier"s transport business is valued at $8.2bn by the deal. The Canadian business will be handed proceeds of up to $4.5bn, including $550m of Alstom shares. Under the terms of a memorandum of understanding signed by the two sides, the Quebec government will give up its stake in Bombardier"s transport arm and become the biggest shareholder in Alstom. The tie-up is not expected to complete until 2021 and will need to be signed off by competition regulators. Alain Bellemare, chief executive of Bombardier, described the sale as a game-changer for the company as it struggles to pay down a crippling $9.3bn debt pile. The deal continues a stream of sell-offs by Bombardier as part of a long-term turnaround plan for the embattled Canadian business. Since taking over in 2015, Mr Bellemare has axed more than 15,000 jobs. Reporting a $1.6bn loss on annual sales last week, which fell 3pc to $15.8bn, Mr Bellemare said Bombardier will transfer its remaining stake in a commercial aircraft unit to Airbus and the Quebec government for $600m. In 2017, Airbus took a 50pc stake in Bombardier’s troubled C-Series small jetliners, with the Quebec government holding 19pc. Developing the jet, which Airbus has since renamed the A220, loaded up Bombardier with debt. The firm sold a wing-making factory in Belfast to Spirit in a $500m deal last year. Mr Bellemare added that the sale of the rail business would allow Bombardier to focus on its private jet business. Buying the Bombardier rail arm will bulk Alstom up, making it the world’s second-largest rail business behind China’s CRCC. However, the sale could face opposition from competition regulators. An attempt by Siemens to merge its Mobility division with Alstom was blocked by the European Commission last year. Analysts at UBS said that Alstom and Bombardier both generate between 60pc and 65pc of their revenues in Europe. But there are limited overlaps between them in the European markets for high-speed rail carriages and signals, UBS said, the two areas which put paid to the Siemens deal Alstom confirmed the talks about a possible acquisition. It said: "Discussions are on-going. No final decision has been made."