Dreamlines, based in Hamburg, has a US-branded website as well as operations in Switzerland, Austria, Australia, the Netherlands, France, Italy, Russia and Brazil and will use Cruise1st to debut in the UK market. The addition of Cruise1st makes Dreamlines the market leader in Australia and Singapore, the company said.

Royal Caribbean Cruises Limited is no longer a shareholder in Cruise1st.

A Cruise1st spokesperson said: "Royal Caribbean is and always has been a valued supplier to the cruise1st and Dreamlines group; customers receive a great benefit from this strong relationship and we expect this to continue. Royal Caribbean will not be a shareholder of Cruise1st anymore."

Daniel Townsley, Cruise1st chief executive, said: “The synergy between Cruise1st and Dreamlines was too great to overlook. Combining a hugely successful global OTA with our own proficiency and database of customers in the UK, Australia and Singapore will drive higher sales volumes and margins and deliver huge growth for the business.”

The Cruise1st brand, its 180 staff and Manchester base will be retained, a spokesperson confirmed.

The combined companies boast sales of more than €320 million, a figure expected to rise to more than €400 million this year, making Dreamlines the largest specialist online cruise agency outside the US.

Dreamlines was founded in 2012 and has more than 400 staff. It has satellite offices in Nice, Amsterdam, Moscow, Sao Paulo and the Gold Coast.

Cruise1st has operated as a web and call centre-based business since 2000 and opened its first “interactive and immersive” cruise retail concept store in Salford in January.

Felix Schneider, Dreamlines’ managing director, said: “Entering the UK, the world’s third biggest cruise market by volume, is an important milestone within our global strategy. We are expanding our role in the market and will strengthen our position as the cruise OTA with the widest global footprint.

“Cruise1st enables us to offer our customers even more unique cruise holiday products and will grow our operator business, a key factor for our future success.”