Endurance Specialty Holdings Ltd yesterday made good on last week’s pledge to seek acquisition of all Aspen Insurance Holdings Limited common stock for a combination of common stock and cash at an improved offer of $49.50 a share.

Aspen closed up two cents (0.04 percent) at $46.34 on the New York Stock Exchange, while Endurance was down 38 cents (0.72 percent) to $52.19.

John R Charman, Endurance’s chairman and chief executive officer, said yesterday: “The commencement of the Exchange Offer today further demonstrates our full commitment to a transaction with Aspen, and provides an additional mechanism for shareholders to support the consummation of this very compelling combination.

“We again call on Aspen’s board and management to act in the best interests of Aspen’s shareholders by engaging with us in constructive discussions regarding our increased proposal and to cease with their rhetoric and entrenchment.”

Meanwhile, Aspen in confirming the Endurance offer, issued this statement: “On June 2, Aspen announced that its directors had unanimously rejected an unsolicited proposal from Endurance with identical terms, noting that the proposal grossly undervalued Aspen, represented a strategic mismatch and, based on conversations with major clients and brokers, would result in significant dis- synergies.

“Moreover, the company noted that the majority of the consideration included in the proposal consisted of Endurance stock, which is highly unappealing.

“As demonstrated by Aspen’s strong first quarter results, the company is delivering on a strategic plan to generate strong growth and shareholder value.

“Aspen achieved strong results across all parts of its business in the first quarter, with a resulting annualised operating ROE of 14.8 percent. The company is well positioned to achieve its 10 percent operating ROE objective in 2014 and to deliver on its expectation that 2015 operating ROE will increase in the order of 100 basis points from 2014.

“In light of Endurance’s formal commencement of an exchange offer, and consistent with its fiduciary duties, the board of directors of Aspen will carefully review the exchange offer in consultation with its independent financial and legal advisers and determine the course of action that it believes is in the best interests of Aspen and its shareholders. The board intends to advise shareholders of its recommendation regarding the exchange offer within ten business days by making available to shareholders and filing with the US Securities and Exchange Commission a solicitation/recommendation statement on Schedule 14D-9.

“Aspen shareholders are advised to take no action at this time pending the board’s recommendation in the Schedule 14D-9.”

Endurance said: “In connection with the improved offer, Endurance on June 2 filed a preliminary solicitation statement with the SEC seeking the support of Aspen’s common shareholders to convene a special general meeting, at which Aspen’s common shareholders would consider a proposal to increase the size of Aspen’s board of directors from 12 to 19 members, which would result in a majority of Aspen’s directors standing for election at Aspen’s 2015 annual general meeting.

“The filing also called for the proposal of a Scheme of Arrangement by Endurance, which will entail the holding of a court-ordered meeting of Aspen shareholders at which Aspen common shareholders would vote to approve a Scheme of Arrangement under Bermuda law pursuant to which Endurance would acquire all of Aspen’s outstanding common shares on financial terms no less favourable than those contained in its increased proposal.”

The Endurance statement yesterday continued: “Under the terms of the Exchange Offer, each holder of Aspen common shares will have the right to receive for their Aspen common shares, at their election: all cash ($49.50 for each Aspen share); all Endurance common shares (0.9197 Endurance shares for each Aspen share); or a combination of cash and Endurance common shares (0.5518 Endurance common shares and $19.80 in cash for each Aspen share).

“The election will be subject to a customary proration mechanism to achieve an aggregate consideration mix of 40 percent cash and 60 percent Endurance common shares (calculated based on the closing price per Endurance common share on April 11, 2014, the last trading day prior to Endurance`s announcement of its initial proposal to acquire Aspen for $47.50 per share).

“The terms and conditions of the Exchange Offer are set forth in the offering documents that Endurance is filing today with the Securities and Exchange Commission.

“The Exchange Offer expires at 5.00pm, Eastern time, on Friday, August 29, 2014, unless extended. The offering documents, including a preliminary prospectus/offer to exchange and a related letter of election and transmittal, describing the Exchange Offer and the means for Aspen shareholders to tender Aspen common shares into the offer will be delivered to Aspen shareholders.”