Some in the car industry have characterized the plant as the most significant investment in British automotive since Nissan came to Britain in the 1980s.
Although the deal has yet to be signed, sources familiar with the matter tell the New York Times that engagement has moved from negotiations to drafting and choreography of how the landmark agreement will be presented.
Tata is considering a new site in Spain and the expected decision to choose Somerset will be presented as a major achievement for the UK government.
Last week, Stellantis, one of the world's biggest carmakers, warned it may have to close UK factories if the government doesn't renegotiate the Brexit deal. The firm, which owns Fiat, Peugeot, Citroen and Vauxhall, had a commitment to making electric cars in the UK but said it was under threat.
The government has conceded that while it does not recognise a figure of 500 m in reported subsidies, it is in the hundreds of millions of pounds.
Tata has extensive steel interests in the UK, including the Port Talbot factory in South Wales, and the government will also offer around 300 m to support, upgrade, and decarbonise those operations.
While government sources conceded that the two projects are not announced at the same time, government sources conceded that the two projects are linked.
Although the price tag is seen as high, the UK is reluctantly involved in a worldwide subsidy war, which has been significantly escalated by the US Inflation Reduction Act - a measure that offers $370 bn 299 bn in sweeteners to companies ready to locate production and supply chains in the US.
Some industry insiders are hopeful that Tata's battery investment will open the door to further battery investments in the UK, which currently has one plant operating next to Nissan's Sunderland factory and one barely on the drawing board in Northumberland.