HONG KONG/LONDON - Vodafone and CK Hutchison are in the final stages of agreeing to merge their British operations, with a long-awaited announcement expected as soon as Friday or early next week, three sources have told Reuters.

The structure of the agreed deal is in line with Vodafone's announcement in October, with the British group owning 51% and Hutchison owning 49%, achieved by adjusting the ownership of debt rather than exchanging cash, one of the sources said.

Including debt the deal could be valued at around 15 billion pounds ($18.6 billion), according to analysts.

Hutchison declined to comment. Vodafone was not immediately available to comment.

The tie-up will create Britain's biggest mobile operator with about 27 million customers, overtaking BT's EE and VM O2, owned by Telefonica and Liberty Global .

The deal will face intense scrutiny from regulators who have previously opposed deals that reduce the number of networks in major markets from four to three.

($1 = 0.8061 pounds)

(Reporting by Clare Jim in Hong Kong and Paul Sandle in London; Editing by Kate Holton)