The deal will create an almost £1bn turnover global BPO giant, capable of creating, managing and delivering campaigns across all media platforms and geographies.

The acquisition, which has been rumoured for the best part of a year, is in response to the growing trend for brands to seek one worldwide provider of marketing services.

"Our complementary business capabilities make Williams Lea and Tag the perfect match. Together, we now have a unique, integrated proposition to meet the marketing services requirements of global brands," said Tim Griffiths, Williams Lea’s group chief executive.

"As the global marketing industry evolves, we are strongly positioned to benefit from the new opportunities it will create."

Tag will continue to operate under its own brand and will become a standalone business division of Williams Lea, which is a subsidiary of Deutsche Post DHL.

Tag chief executive, Steve Parish, who will retain his role, said: "This deal, we believe, is a paradigm shift for the industry. Tag has always been at the forefront of driving change and efficiency and it is essential for that to continue.

"In order to take the company to the next level, we need to be able to offer both a broader range of services and a bigger geographical footprint. This deal gives us all this, as well as the scale to deliver unique, end-to-end, marketing solutions."

Bruce Edwards, chief executive of DHL Supply Chain and a board member of Deutsche Post DHL, added: "By combining these two businesses, we are taking advantage of the enormous growth opportunities in the global marketing services market.

"We expect the combination of Williams Lea and Tag to have a sustainable positive impact on our earnings and at the same time enhance our ability to customise global solutions for our clients."