Asked by Sky News how many jobs would be lost in no-deal scenario, Clark said: "It's many thousands of jobs".
The veteran MEP noted that Theresa May still has a couple of weeks left before her premiership is expected to terminate, and that she could "as a parting gift, still appoint a new ambassador who might be perfectly very bad like Sir Kim Darroch", but that if the decision does fall to Mr Johnson, and Mr Johnson does make the offer, he might not be able to accept it.
"All too often, those who see it as a position of power see it as about themselves and not about the people they are serving", she said.
"There is a real difference".
His comments came after former prime minister Sir John Major said he would seek a judicial review if Mr Johnson tried to suspend parliament to force through a no-deal Brexit.
May stepped down from being Conservative Party leader after her failure to get Parliament to approve a plan for Britain's departure from the European Union.
The victor, and new Prime Minister, is expected to be announced on July 23.
She added it's unlikely that her successor will negotiate further Brexit concessions from the EU. "And I have accepted that", she told talkRADIO's Julia Hartley-Brewer.
Britain's Prime Minister Theresa May leaves 10 Downing Street for her weekly Prime Minister's Questions at the House of Commons in London, Wednesday, July 10, 2019.
Lady Hayter, deputy Labour leader in the House of Lords and the shadow Brexit minister, told BBC Radio 4's Today programme: "Clearly in the House of Lords we tend to take our responsibility to look after the constitution quite seriously, and a part of this is in making sure that on an enormously important issue like Brexit, parliament is taking the decisions and not just government".
"If a male Prime Minister's voice had broken up, it would have been said "what great patriotism, they really love their country".
As THE Conservative leadership race reaches its final stages, the two remaining candidates, Boris Johnson and Jeremy Hunt, attended the Cardiff hustings on 6th July to make their case to the party membership, for who should be the next leader.
A Guardian survey of voting Tory members, shows that Boris Johnson already has enough cast votes to win the PM runoff over Jeremy Hunt.