UN climate talks must go ahead in June even if negotiations are held virtually, Britain's president of the COP26 summit said Tuesday, despite "valid concerns" over the lack of in-person dialogue.

In an open letter to countries party to the UN Framework Convention on Climate Change (UNFCCC), Alok Sharma said a formal session of technical talks was needed to lay the groundwork for the "unprecedented" to do list at COP26, set for November in Glasgow.

He said that Covid-19 restrictions would likely mean the session, which is traditionally held at UNFCCC headquarters in the German city of Bonn, would likely take place online. 

This is despite concerns raised by several countries that virtual talks could prejudice their position as equal parties to richer emitters at the crucial negotiations. 

"The UNFCCC are taking the necessary steps to accommodate those challenges, including connectivity, working across time zones, and group coordination," Sharma wrote.

COP26 was originally scheduled for November 2020 but was pushed back due to the pandemic. 

There are fears that some countries will be unable to attend the talks in person due to sluggish or non-existent vaccination campaigns.

Sharma again indicated his strong preference for COP26 to take place "in person" but stressed that delegates needed to arrive in Glasgow "having done our homework".

The laundry list facing participants in Glasgow is daunting. 

Delegates are faced with ever-direr warnings from scientists about the scale of emissions cuts needed to keep within reach the goal of limiting global warming to 1.5C -- as laid out in the Paris agreement. 

That deal, struck more than five years ago, committed nations to resubmit their emissions cutting plans -- known as NDCs -- every five years with enhanced green ambition. 

Yet many of the largest emitters have so far failed to do so and countries have not even agreed on a unified rulebook governing how the Paris agreement works in practice. 

Sharma said COP26 must see "substantive decisions" on the thorny issue of emissions trading and accounting, as well as significantly ramping up finance to climate vulnerable nations to help them adapt to the warming world. 

The UN says that emissions must fall nearly eight percent annually to keep 1.5C in play -- equivalent to the emissions saved during the pandemic every single year through 2030. 

Sharma hinted that an additional negotiating session may be needed to get countries closer together before Glasgow, "in person, should it be feasible".

"Such an approach to formal sessions and capturing progress is, in my view, the only way we will make sufficient progress ahead of meeting in person in Glasgow to ensure COP26 delivers on its mandates and what the world expects of us," he said.