In a strongly-worded letter to HKEX chief Charles Li, the London exchange operator says it was "surprised and disappointed" that HKEX went public with its offer just two days after making an initial approach.

LSE chair Don Robert goes on to contrast the merits of the Exchange's £27 billion bid to buy market data operator Refinitiv - "the culmination of many months of strategy development, deep consideration and discussion" - with HKEX's offer.

"Our planned acquisition of Refinitiv meets LSEG’s strategic objectives across its businesses which the Board believes to be critical for a leading Financial Markets Infrastructure provider of the future," he writes. "In stark contrast, the high geographic concentration and heavy exposure to market transaction volumes in your business would represent a significant backward step for LSEG strategically."

He also takes a swipe at HKEX's promise of a swift transaction, pointing out the regulatory barriers that would likely be erected for the merged entity.

"Your assertion that implementation of a transaction would be “swift and certain” is simply not credible," he states. "On the contrary, we judge that the approval processes would be exhaustive and that support from relevant parties, vital for the transaction, is highly uncertain. This would pose serious risk for our shareholders."

HKEX's valuation is also way off-kilter, he continues, and with the composition incorporating a share exchange amounting two-thirds of the price, would represent a significant leap of faith by shareholders given the ongoing turmoil in Hong Kong

"Given the fundamental flaws in your proposal, we see no merit in further engagement," Robert concludes.