The company has cautioned that a provisional agreement between negotiators in the UK and Brussels is yet to be approved by parliaments on both sides of the Channel, and could fall apart.
In a statement, the LSE said: “Brexit negotiations between the UK and the EU continue but the UK’s final exit terms are still unclear.
“The group is executing contingency plans to maintain continuity of market function and customer service in the event of a hard Brexit.
“These contingency plans include incorporation of new entities in the EU27 and applications for authorisation within the EU27 for certain group businesses.
“However, the complexity and the lack of clarity of the application of a hard Brexit may decrease the effectiveness or applicability of some of these contingency plans.”
The firm said that although a draft withdrawal agreement had been drawn up by both sides, with plans for a 21-month transition arrangement after Article 50 is triggered in March 2019, this agreement could not be relied upon at the current stage of negotiations.
For the six months ended June 30, the LSE’s revenue grew up 12 per cent to £953 million, up from £853 million at the same point last year.
Operating profit was up 29 per cent from £305 million to £393 million, helping lift shares 2.6 per cent or 115p to 4,472p.
David Schwimmer, who was named as the LSE’s new boss in April, said: “I am delighted to join the group, which continues to deliver strong growth.
“The group’s strategy, based on an open access and customer partnership approach, provides a great foundation for further success.”