Boris Johnson was fielding questions in parliament about the UK leaving the EU on Tuesday when a euroskeptic Conservative ally, Philip Hollobone, urged him to tell leaders in Brussels that they could "go whistle" if they wanted "a penny piece more" than the money the UK had already paid to the EU since joining in the 1970s. 

"I am sure that my honorable friend's words will have broken like a thunderclap over Brussels," Johnson began in response. "He makes a very valid point, and I think that the sums that I have seen that they propose to demand from this country seem to me to be extortionate, and I think that to 'go whistle' is an entirely appropriate expression." 

Another MP could be heard issuing a brief wolf whistle as Johnson concluded his comment. 

The question of a so-called "divorce bill" for the UK leaving the EU is among the top items on the negotiating agenda. Some reports have put a possible bill as high as 100 billion euros, although mooted costs have varied wildly. The UK government has distanced itself from all reported figures, but has said it intends to settle its "obligations" on leaving.

Johnson also told the House that the government was confident of reaching a deal with Brussels and that it had "no plan" for a breakdown in negotiations. 

"There is no plan for no deal because we are going to get a deal," the foreign secretary said. However, one of Theresa May's preferred election soundbites had been: "No deal is better than a bad deal."

Clash with May's gig economy speech

Johnson's comments might have displeased Prime Minister Theresa May, seeing as they coincided closely with a keynote speech of hers designed to steady the ship after the disappointing election.

May attempted to reassert her leadership and called for unity in the face of Brexit at the Tuesday unveiling of a major report into worker conditions she commissioned a year ago as she took leadership.

May used the launch to urge her political opponents to help "fulfill the promise" of Britain's departure from the European Union as she attempted to relaunch her minority Conservative government's agenda and her early, briefly-popular calls to support Britons who were "just about managing."

She said she remained determined to "take big decisions in the long-term interests of Britain, so that we ... are better able to seize the opportunities ahead as we fulfill the promise of Brexit together."

May, who faces particular difficulty passing legislation through parliament and destabilizing discontent within her party after a disastrous election result, issued a direct challenge to opposition parties to work with her government to improve employment conditions in the UK.

May acknowledged that the election result was "not what I wanted," but said she remained committed to building a fairer Britain as the country leaves the EU. She said the vote to leave the EU showed a deep dissatisfaction among British voters, but did not reflect in detail on how she lost her majority.

"In this new context it will be even more important to make the case for our policies and values," she said, asking other parties to contribute their ideas.

Run out of steam

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Labour leader Jeremy Corbyn said May's plea for cooperation showed the government had "run out of steam at a pivotal moment for our country and the world."

"The prime minister now heads a zombie government that has no ideas, no answers and no leadership," Corbyn said."Her premiership has run out of steam and she will soon have to deal with her own insecure employment."

Dependent contractors

The worker conditions report by Matthew Taylor, a former adviser to Tony Blair and Chief Executive of The Royal Society of Arts, recommended additional protection for workers in the face of vanishing job security, particularly in the so-called gig economy.

The report called for the creation of a new category of worker - the "dependent contractor" - to improve conditions for people working for companies such as Uber and Deliveroo.

May said she was hoping to strike a balance between protecting employee rights, and ensuring the viability of businesses, saying she wanted to avoid "overbearing regulation," while making sure "employees have the protections they need."

"Legislation is not always the answer," she told a press conference.

Read: Theresa May: A dead woman walking?

Opinion: Theresa May's devastating miscalculation

S&P: UK outlook still negative

May's calls for cooperation came as ratings agency Standard & Poor's gave the country a sobering assessment ahead of Brexit, with growth set to slow from 2016's 1.8 percent to 1.4 percent this year and 0.9 percent or less the next year.

The agency, which stripped the UK of its top-notch AAA credit rating soon after the Brexit referendum, kept its official "outlook" for the UK as "negative." This means that a further downgrade is conceivable, perhaps in the short term. 

"Our forecasts for slower growth are subject to considerable downside risks, stemming mainly from Brexit uncertainties," senior economist Boris Glass said.

Glass said the situation would be even more precarious should talks with the EU stall and they end up with a hard Brexit.