Aspen Insurance Holdings Ltd says it has found “overwhelming consensus” among shareholders for rejecting Endurance Specialty Holdings’ $3.2 billion bid for the company.

However, that is disputed by Endurance which argued yesterday that shareholders of both companies that it has approached agree that the combination of the companies would make sense.

The two Bermuda companies have been trading sharp criticisms of each other since Endurance revealed its $47.50-per-share hostile takeover bid at the start of last week.

Since then Aspen has announced a ‘poison pill’ rights plan that would allow its shareholders to buy shares at a discounted price in the event of a third party acquiring a stake of ten percent or more of the company’s shares. The plan is designed to deter Endurance by making any takeover substantially more expensive.

Endurance’s shares rose 62 cents, or 1.2 percent, to close at $51.55 in New York yesterday, while Aspen shares gained seven cents, or 0.2 percent, to reach $44.52.

In a statement released late on Sunday, Aspen said chairman Glyn Jones and chief executive officer Chris O’Kane had sent out a letter to shareholders yesterday detailing why Aspen’s board of directors had rejected the cash-and-stock bid from its Bermuda rival.

“Since Endurance publicised its letter to Aspen on April 14, we have actively reached out to shareholders and have found overwhelming consensus for our rejection of Endurance’s ill-conceived ‘proposal,’ which undervalues Aspen, represents a strategic mismatch and carries significant execution risk,” Aspen chairman Glyn Jones said in the statement. “Furthermore, our discussions with clients and brokers have confirmed our view that the combination would result in substantial dis-synergies.”

In the letter, Mr Jones and Mr O’Kane unleashed a thinly veiled attack on the management style of Endurance chairman and chief executive officer John Charman, who joined the company last May.

“We have serious concerns about the significant personnel disruption and loss of attractive business that would result from a combination of Aspen’s collaborative, teamwork-oriented culture with Endurance’s centralised, top-down management model,” the letter stated.

“Endurance’s recent description of its ‘collegial environment’ is inconsistent with the industry’s experience. Aspen is currently in litigation as a result of Endurance’s orchestrated poaching of Aspen employees, and, according to news reports, Mr Charman was relieved of his positions at his last two companies for his less than collegial attitude — reportedly leaving Ace due to ‘personal differences’ and Axis when the ‘board kicked him out in 2012 without cause’. (SNL Insurance Daily, 23rd August 2013).

“Yet, now Endurance assures our and its own shareholders that a business where the most valuable assets are its people will thrive, and that the merging of the two cultures will proceed smoothly, in the ‘collegial environment’ established under Mr Charman’s leadership.”

Endurance yesterday dismissed Aspen’s statement as “defensive” and hit back at the comments on the organisation’s culture, arguing that the senior staff Endurance has recruited during a major overhaul over the past year speaks for itself.

“The significant inflow of world-class talent that Endurance has attracted in the past year from across the industry is a strong testament to the winning culture it has created,” Endurance stated.

“The combined company will have greater scale and market presence that will create expanded opportunities. In the face of that, assertions about cultural issues and dis-synergies impeding the operation of the combined company are unfounded.”

Endurance said Aspen was continuing “to deny its shareholders the ability to receive a highly attractive premium and an ongoing stake in a global industry leader”.

Endurance chief financial officer Michael McGuire said: “Endurance remains clearly intent on consummating a transaction and not, as Aspen claims, just ‘kicking the tyres’.

“Aspen well knows that customary due diligence is no roadblock and would not present any impediment to closing a negotiated transaction. Moreover, the broad range of Aspen and Endurance shareholders with whom we have been speaking agree with the strategic rationale and financial benefits we outlined. This stands in stark contradiction to Aspen’s mischaracterisation of market sentiment, which we strongly question.”

Another point of contention between the Bermuda rivals was Aspen’s claim that Endurance has shown “disdain” for the Lloyd’s of London market, where Aspen runs a syndicate.

“Endurance has expressed a strong dislike for Lloyd’s business,” Mr O’Kane and Mr Jones wrote to shareholders. “In an attempt to convince the market that Endurance would embrace Aspen’s top tier Lloyd’s business, John Charman, Chairman and chief executive officer of Endurance, stated on 14th April that ‘Aspen’s core strength in the London insurance market — including through Lloyd’s — is an attractive area’.

“This is in stark contrast to Endurance’s previously expressed disdain for Lloyd’s, including less than a year ago when Mr Charman stated, ‘I find it difficult to want to be a ... piece of [Lloyd’s].’ (Insurance Insider, 10th June 2013).

“Given such statements, we would be extremely concerned that a combination with Endurance would pose risks to our Lloyd’s syndicate, which is one of the most dynamic parts of our insurance franchise and a top performer amongst Lloyd’s syndicates.”

Endurance countered that it had “unparalleled Lloyd’s expertise and insight”.

“Mr John Charman has 30 years of experience in Lloyd’s, including as founder of the first Lloyd’s syndicate backed by corporate capital and as senior deputy chairman at the Council of Lloyd’s during its financial crisis,” Endurance stated.

“Try as Aspen may to distort a year-old comment, the fact remains that he is and has always been a strong supporter of a well capitalised, larger Lloyd’s operation, which is what the combined Endurance-Aspen platform would be.”

Endurance also pointed out that its directors and managers had a much greater stake in their company than was the case at Aspen.

“Aspen simply cannot assert meaningful alignment of interests with shareholders given the paucity of the board and management’s ownership stake, both individually and collectively,” Endurance stated. “This contrasts dramatically with chairman and CEO John Charman’s substantial ownership stake in Endurance as well as his commitment to purchase $25 million of additional shares in connection with the transaction. In fact, insider ownership of Endurance totals 4.7 percent vs 1.4 percent for Aspen, a sharp disparity.”