Slaughter and May and Davis Polk & Wardwell have been instructed by Shire to advise the UK pharmaceutical giant on a £27bn unsolicited takeover bid from US drugmaker AbbVie.

AbbVie, whose offer was formally announced today (20 June), has until 18 July to make a formal bid, according to Takeover Panel rules.

The US raider has turned to Herbert Smith Freehills in the UK and Europe and Sullivan & Cromwell in New York for advice.

Shire immediately rejected the "highly conditional" offer, which its board said undervalued the company, and would involve the creation of a US listed holding company with a UK tax domicile.

Slaughters corporate partners Martin Hattrell and M&A head Stephen Cooke are leading for Shire on English law matters, alongside partner Adam Eastell and corporate associates Paul Mudie and Emma Plaxton.

The Slaughters team is working with Davis Polk partners Bill Chudd and M&A global co-head George 'Gar' Bason in New York, who advise the company on all major US law matters.

Both firms are long-time corporate advisers to the FTSE 100 company, having jointly advised on a number of deals and financings, including the company's $4.2bn acquisition of rare disease company ViroPharma last year.

An HSF team featuring partners Gillian Fairfield, James Palmer, global M&A head Stephen Wilkinson and senior associate Adam Charles are advising AbbVie.

The firm previously advised the client on a number of high-value patent and licensing disputes in the UK and Europe concerning its anti-inflammatory drug Humira.

On US law matters, AbbVie has instructed Sullivan & Cromwell's New York-based healthcare and life sciences co-head Matthew Hurd.

The proposed takeover follows Pfizer's failed bid for another UK pharmaceuticals company, AstraZeneca, earlier this year. That deal saw roles handed to Freshfields Bruckhaus Deringer and Skadden Arps Slate Meagher & Flom.

Davis Polk also acted on that takeover, with corporate partner Paul Kingsley advising AZ on corporate aspects.

Last year's $34bn shareholder carve-out of Abbott Laboratories yielded roles for Baker & McKenzie Matheson, and Wachtell Lipton Rosen & Katz.