The forecast was revealed today in the annual review of the tourism agencies, which previously did not expected to break the 40 million barrier until 2020. Overseas visitor spend is also predicted to reach a record £26.3b.
Last year the number of inbound visits increased by 4% to 39.2 million, with visitor spend up 9% to £24.5b.
Minister for tourism Michael Ellis said: "Britain's tourism industry is booming. Last year was a very strong year for domestic and inbound tourism, with tens of billions of pounds going into our economy.
"The government, alongside VisitBritain/VisitEngland, is working with the sector to build on this success with an emphasis on attracting major business events and investing in local tourism projects through the Discover England Fund.
"Tourism shows the world the best of our nation. As we approach the UK's exit from the European Union, we are absolutely committed to helping the industry continue to grow, promoting the country as a must-visit destination and ensuring that local communities benefit."