As U.K. Prime Minister Boris Johnson vowed he'd rather die thandelay Brexit, the nation's merger watchdogs were quietly gatheringinformation on a few key transactions they thought they'd have tovet if Britain crashed out of the European Union (EU) onHalloween.

But on Tuesday, with Brexit on hold and plans for a Decembergeneral election taking shape in London, the CEO of the nation'sCompetition and Markets Authority (CMA) hinted at a modicum offrustration over another false alarm as he spoke at a Brusselsantitrust conference.

"The situation essentially changes day by day," said AndreaCoscelli, who runs the CMA, when asked about the Brexit situation."You know as much as I do."

A U.K. exit from the European Union without a legal accord wouldinstantly force Britain's merger authority to take charge ofseveral big deals handled by the European Commission in Brussels.While the U.K. does examine some smaller mergers, largetransactions between companies that generate significant revenue inseveral European countries almost always go to EU regulators.

"We were preparing for a possible no-deal outcome; it wasclearly a material possibility," Coscelli told the GlobalCompetition Review event. "We identified a handful of transactions"in the EU system "that would come to us with no-deal exit and forwhere, for a variety of reasons, we felt it was an important U.K.nexus and we wanted to play a major role in them."

Coscelli didn't name the companies that are engaging with theCMA on a potential review. Some "have been very open to it; otherswere a bit more cautious," he said, as the U.K. doesn't technicallyhave jurisdiction to rule on these transactions as thingsstand.

London Stock Exchange Group Plc's proposed takeover of data firmRefinitiv is one tie-up that may need a separate U.K. review in ano-deal scenario, according to Bloomberg Intelligence analyst AitorOrtiz.

Regulators want to "really try to do enough to make sure that ifcertain scenarios play out, companies are not in a difficultposition," Coscelli said. "Our pitch was very much: It is in yourinterest to engage with us because obviously if you suddenly end upwith U.K. jurisdiction, it's not particularly helpful.

"If this week plays out the way it looks like—so we end up nowwith a three-month extension essentially—we're going to go back andlook at this list and see whether anything needs to change," hesaid. "My working assumption is that we continue this process.

"As things stand, the U.K. could still crash out with no deal atthe end of January, or depending on the outcome of a possibleelection that might happen or not between now and then. So it isclearly very complicated."

Coscelli sounded disheartened when asked whether the CMA waschanging any of its merger rules, beyond a proposal for an overhaulearlier this year.

"Things are changing too fast really to sit down and think," hesaid. "You need a long time period to change policies, it's assimple as that."

–With assistance from ChristopherElser.

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