Speth reiterated a previous warning over a hard Brexit scenario hitting the Tata Group-owned company's annual profits by over 1.2 billion pounds, which might even force its exit from the UK.
"At the end of the day we are British. We are an absolutely British company and we want to stay here," he said.
JLR is among a number of companies participating at the Zero Emission Vehicle Summit, during which Prime Minister Theresa May announced a 106-million-pound grant to support research and development in green vehicles, new batteries and low carbon technology.
Speth said electric and autonomous vehicles represented a "huge opportunity" but stressed that the UK government must collaborate more closely with business on the sector.
Back in July, the JLR CEO had issued a similar statement warning the UK government against a "bad Brexit deal". The UK's largest carmaker has witnessed a complete turnaround in its fortunes since Tata Motors acquired the traditional British brands from Ford 10 years ago.
Speth had highlighted that under Indian ownership, the company has spent around 50 billion pounds in the UK in the past five years, with plans for a further 80 billion pounds in the next five. However, all that could be put in "jeopardy" with a bad deal with the EU as Britain prepares to exit the 27-member economic bloc in March next year.
At the beginning of the year, JLR had said it would cut production at its plant in Halewood, Merseyside, where it builds three of its Range Rover models. In April, it said that it would not renew the contracts for 1,000 temporary workers at its operation at Solihull in the West Midlands region of England.
But the company had also revealed plans to invest in the Solihull site to allow it to build its new Range Rover models, some of which will be electric-powered, from 2020.
In June, JLR said it would shift production of its Land Rover Discovery SUV to a new plant in Slovakia, potentially leading to some job losses in the UK.
The company's repeated Brexit interventions come in the wake of similar statements by other manufacturing giants like BMW and Airbus, warning against a "no-deal" Brexit.