Bloomsbury, publisher of the best selling Harry Potter children's books, has moved to bolster its reference division by agreeing to buy the long-established publisher of the Who's Who directory and Blue Guide travel books for £16.4m.

A&C Black has recommended Bloomsbury's offer of 1.47 shares for each of its own, which values its shares at 1,025p each. There is a cash alternative of 985p for each Black share.

One of the main beneficiaries of the deal will be BBC chairman Sir Christopher Bland, whose 9% stake in Black is valued at £1.5m.

Black's book list includes the Writers' and Artists' Yearbook, Black's Medical Dictionary and a number of children's titles. Chairman Charles Black said he had asked Bloomsbury to buy the 113-year-old business because of its marketing and electronic publishing expertise.

Bloomsbury's chief executive, Nigel Newton, expects the deal to lead to production cost savings, while greater cash flow from the combined group would al low increased investment in acquiring rights, identifying and nurturing new authors.

He will need to invest in digitising Black's content, and Bloomsbury said it planned to raise £2.75m through a placing of new shares at 670p each.

Shares in Black have underperformed its sector over the past year and many analysts have viewed it as a sleepy operation in need of a shake-up. Black's shares shot up 118% or 515p to 950p on the announcement of the offer.

Kit van Tulleken, of pub lishing mergers and acquisitions specialist the van Tulleken company, said: "A&C Black is a very elegant publishing house with an excellent staff and imprints but it has remained a hidden gem and never really pushed itself. I'm sure it will benefit from Bloomsbury's marketing expertise."

Bloomsbury shares, which have quadrupled in value over the past 12 months largely due to strong sales of the Harry Potter series, written by JK Rowling (pictured), closed off 2.5p at 695p.