US Edition A takeover would radically strengthen the UK bourse, which is trying to build up a dominant presence in the market for derivatives and only recently suffered a setback when its proposed merger with Canadian exchange TMX failed.
A bid would also pit the LSE against rivals Markit and Nasdaq OMX, which have both previously expressed an interest in the clearing house.
LCH.Clearnet is owned 83pc by its bank and broker customers and 17pc by NYSE Euronext and the London Metal Exchange.
It has become an increasingly attractive target since the financial crisis as regulators have signalled they want to bring a lot of over-the-counter trading in derivatives onto supervised exchanges.
In a statement, the LSE said confirmed it was "in discussions" with LCH.Clearnet regarding a potential transaction.
"These discussions are at an early stage and there can be no certainty that any action or agreement will result."
Clearing houses are a vital part of the infrastructure by standing between buyers and sellers and providing a guarantee that the deal will complete. LCH.Clearnet is particularly strong in interest-rate swaps, a large and expanding part of the derivatives market.
The more that is brought on exchange, the more clearing there will have to be, potentially delivering rapid growth.
The LSE has signalled its plans to move into the area, having launched a fledgling derivatives business in June.
A takeover would fit with the board's strategy to broaden the business, and a merger would also give it a stronger platform from which to compete with Deutsche Borse and NYSE Euronext, which are planning to merge.
It is the second time in six months that LSE has engaged in talks with LCH.Clearnet.
The bourse denied a transaction was being discussed in May despite tentative talks as it was then wholly focused on the TMX merger. At the time, Markit and Nasdaq OMX also expressed their interest.