His role will be to "develop and negotiate free trade agreements and market access deals with non-EU countries", they said in a statement, suggesting that the government plans to leave the single market following Brexit.
The EU's negotiator Michel Barnier dismissed the suggestion of postponing the negotiations and said such a delay would only prompt further instability.
"I got us into this mess, and I'm going to get us out", she said.
A spokesman for his Department for Exiting the European Union said Britain had been "crystal clear" about its approach. It could also refuse to start negotiations on a future trading relationship before exit terms are agreed. We are clear this is what is set out in Article 50.
"We also respect the other parties' mandates, we want to get back to an executive that has all the parties around the table to collectively take decisions".
UK PM Theresay May said today that no deal could be struck on exiting the European Union unless the future relationship with the bloc was taken into account.
The spokesman added that although some issues would be given early priority "the withdrawal and future are intimately linked".
Working groups were to take place later to focus on three key areas - the status of European Union citizens living in Britain and British citizens living in the European Union; the divorce bill for Britain; and the status of the Northern Irish border with Ireland. "The European citizens in the United Kingdom, we want to get on with as fast as possible because we don't want people to be in a state of anxiety".
"We remain fully committed to making the institutions work", she said.
Fears, frustrations grow as death toll in London building fire rises
London Fire Commissioner Dany Cotton said her crews had identified a "number" of those killed, "but we know there will be more". Very early in the morning on Wednesday, a fire erupted in high rise apartment building Grenfell Tower in West London .
In his Mansion House speech, Hammond was expected to make the case for a so-called "soft" Brexit, which prioritises economic considerations over the more "hard" Brexit approach, which focuses more on limiting immigration and restoring sovereignty.
Of course, the government is not only beleaguered by its post-election hiatus but by the growing anger over its response to this week's Grenfell Tower fire disaster - with May criticized for failing to meet victims' families and politicians facing anger in the streets from local residents.
Almost a year to the day since the United Kingdom voted to leave the European Union, the process of Brexit finally begins on Monday.
While Monday's session is billed as "the opening of negotiations at the political level" - with citizens' rights, the financial settlement, the Northern Irish border issue and more due to be discussed - in reality the meeting will mostly be a more formalized continuation of the "talks about talks" that have been underway for weeks.
It follows a meeting in Brussels on Thursday where both sides agreed that the formal negotiations under the Article 50 process can now commence.
She needs DUP support to cling to power after her election fiasco, leaving the European Union's Brexit negotiator wondering when divorce talks will begin. "I can't negotiate with myself", he told the Financial Times newspaper.
He said they should drop their claim that "no deal is better than a bad deal", warning: "No deal has never been a viable option".
Barnier's interview will heap yet more pressure on May, who called a snap general election to give her a stronger hand at the Brexit negotiating table.