Jaguar and Land Rover have lost a combined £673.4 million in the past year - a sharp drop from its £641.5m profit in the same period last year.
Furthermore, the "total recognised losses" at JLR - including actuarial and other losses related to the firms' pension schemes - reached nearly £1.2bn last year.
However, a JLR spokesman stressed that the accounts relate to its UK operations only, and added that the previous financial year's results had been boosted by a sharp rise in its Aston Martin shares, which have now been sold on.
The news comes as JLR and their owner, India's Tata Motors, strive to conclude long-running and increasingly acrimonious talks with the British government over short-term financing.
According to reports in the Financial Times newspaper the government says it is only prepared to offer JLR a guarantee for a £175m commercial bridging loan, which is significantly less than the £500m that Tata has been seeking.
Furthermore, Tata is pushing for a 12-month term for the loan, while the government wants a six-month deal.