Britain’s biggest drugmaker is preparing to build new drug testing facilities in Europe as part of detailed plans in in the event of a failure to agree a Brexit deal.

GlaxoSmithKline chief executive, Emma Walmsley, said drug companies needed clarity on future relations with the EU as soon as possible to minimise disruption to medicine supplies. Walmsley also repeated her earlier call for a transition period of at least two years.

“The most important thing is to get to clarity on an implementation phase for at least two years, potentially longer, but to get clarity on that as soon as possible,” she said.

The company is not planning to move operations out of the UK, but if no deal is reached, it will duplicate certain facilities in Europe, allowing it to retest drugs manufactured in Britain and shipped to the continent.

Walmsley said: “We are not thinking of any relocation out of the UK, but … we are looking at contingency planning in terms of testing facilities, to allow us to have as seamless a transition as possible, and make sure we are providing secure supply to the patients that need our drugs and medicines.”

She added: “All of that work is under way in the detailed planning group, and we will be ready for it as necessary.”

GlaxoSmithKline’s requests to the government also include making sure the UK can participate in the EU regulatory framework, setting up a talent-friendly immigration policy and delivering predictable funding levels for UK sciences.

Walmsley’s comments followed a warning from Japanese carmaker Toyota that the government needed to “lift the fog” surrounding Brexit negotiations. Toyota said uncertainty over the UK’s post-Brexit trading relationship with the EU was hindering its ability to plan for the future of its business in the UK, where it employs about 3,000 people.

“The UK government should … understand that we cannot stay in this kind of fog when we don’t know what will be the output of the negotiation,” said Didier Leroy, executive vice-president at Toyota.

“As quick as we can get clarity on that, better will be the way we can prepare [for] the future.”

On Wednesday the City of London warned that financial businesses would start activating Brexit contingency plans unless there is a transitional deal by the end of 2017.

In a letter to the chancellor, Philip Hammond, Catherine McGuinness, the most senior policy official at the City of London Corporation said the UK was facing a “historically defining moment” and warned that the timetable for business to prepare for transition was “tightening very rapidly”.

Earlier this week five of the UK’s biggest business lobby groups, including the CBI and British Chambers of Commerce, wrote to the Brexit secretary, David Davis, urging him to quickly establish a transition deal that mirrored existing arrangements, or risk losing British jobs and investment.