Pharmacy giant Alliance Boots has sold 55% of its business to the US pharmacy company Walgreens in a £9 billion deal.

The deal which is expected to be completed in the first quarter of 2015 will see Walgreens keep its headquarters in the US amid increased scrutiny from US tax authorities as it does not qualify for a controversial tax inversion.

Chief executive Greg Wasson said: “We took into account all factors, including that we could not arrive at a structure that provided the company and our board with the requisite level of confidence that a transaction of this significance would need to withstand extensive IRS review and scrutiny.”

The merger is expected to deliver over $1 billion in cost savings by the end of 2017 and will also create an estate of 11,000 stores across 10 countries with 350,000 staff employed.