Business Secretary Greg Clark said the Government is determined to ensure JLR, a "great British success story", can continue to "prosper and to invest in Britain".
Dr Ralf Speth, chief executive of JLR said the company's "heart and soul was in the UK".
He said: "However we, and our partners in the supply chain, face an unpredictable future if the Brexit negotiations do not maintain free and frictionless trade with the EU and unrestricted access to the single market.
"We urgently need greater certainty to continue to invest heavily in the UK and safeguard our suppliers, customers and 40,000 British-based employees.
"A bad Brexit deal would cost Jaguar Land Rover more than £1.2 billion profit each year.
"As a result, we would have to drastically adjust our spending profile. We have spent around £50 billion in the UK in the past five years, with plans for a further £80 billion more in the next five.
"This would be in jeopardy should we be faced with the wrong outcome.
"For more than 250 years, since the era of Adam Smith, Britain has championed free markets and made the case for free trade.
"If the UK automotive industry is to remain globally competitive and protect 300,000 jobs in Jaguar Land Rover and our supply chain, we must retain tariff and customs-free access to trade and talent with no change to current EU regulations."
Dr Speth added: "Electrification and connectivity offer significant economic and productivity opportunities - get Brexit wrong and British people, businesses and broader society lose the chance to lead in smart mobility."
More than 40,000 workers are employed by JLR in the UK, with a further 260,000 jobs in the UK supply chain.
In 2017 the company sold 621,000 cars, with 80% of them going to 130 countries.
One in three cars exported from the UK are Jaguars or Land Rovers.
Mainland Europe is one of JLR's largest markets, with 20% of cars being sold there.
In the current financial year JLR intends to invest £4.5 billion, with more than half going into development of new vehicle models and technologies.
Jaguar Land Rover's UK tax contribution exceeds £2 billion a year.
Mr Clark tweeted: "JLR is a great British success story. We are determined to make sure that it can continue to prosper and to invest in Britain."
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