Source: Sharecast
The Competition and Markets Authority said the tie-up could lead to a worse user experience, a more limited range of products and/or higher prices for British consumers.
As a result, it wants Spreadex to agree to offload the business, otherwise it will impose an order requiring its sale to a CMA-approved buyer.
A Spreadex spokesman told Reuters: "Spreadex strongly disagrees with this entirely disproportionate decision and are reviewing all available options."
Spreadex acquired the rival spread betting firm from French lottery operator FDJ in 2023 for an undisclosed sum.
Following an initial probe, the CMA concluded in 2024 that the tie-up would likely "substantially lessen" competition. Spreadex appealed to the Competition Appeal Tribunal, however, which in turn referred the decision back to the CMA for reconsideration in March this year.
The CMA said that since then it had obtained further evidence, which had led it to conclude a monopoly had been created.
Richard Feasey, chair of the independent panel reviewing the merger, said: "We found that the merger substantially lessens competition by removing Spreadex’s only competition in the sports spread betting market in the UK.
"We also found that the only effective remedy would be for Spreadex to sell Sporting Index, to restore competition."
Privately-owned Spreadex was founded in 1999 by former City trader Jonathan Hufford.