As the Brexit talks were due to resume on Monday, Corporate Europe Observatory (CEO) and Global Justice Now claimed the Brexit agreement is "not only being shaped at the negotiating table, but also by the lobbyists who are trying to influence each side's position papers."
Data gathered by the two pressure groups claims that the meetings with ministers from the UK's Department for Exiting the EU (DExEU) and members of the EU's Brexit task force shows a "common willingness to privilege the representatives of corporate interests above all others."
It is claimed that between October 2016 and March 2017, DExEU staff had six meetings with big business representatives for every one meeting with an NGO, a trade union or a think tank.
According to CEO, "This figure may even just be the tip of the iceberg, as Brexit lobby meetings are also likely to take place with DExEU officials not required to disclose meetings."
The DexEU list of lobby meetings allegedly includes several actors who have previously made financial contributions to the UK Conservative party's head office, as well as corporations with revolving door links to senior party figures.
CEO claims, "The corporate bias in the lobby meetings of DexEU mirrors the pattern of lobbying seen at the UK Department for International Trade.
"The ministers developing the UK's post-Brexit trade relationships with the rest of the world have been holding 90 per cent of their lobby meetings with representatives of business interests."
It is also alleged that the team of chief EU Brexit negotiator Michel Barnier had 10 meetings with corporate lobbyists for every one NGO they met between October 2016 and May 2017.
CEO, which is based in Brussels, states, "The full list of meetings highlights just how rarely citizens and smaller businesses have been heard by the negotiators, despite the fact that the Brexit deal will directly affect the everyday lives of all UK residents and the country's many small and medium-sized businesses."
The research also highlights that both the UK and EU negotiators "withhold participant lists, agendas, minutes and all other documents from their lobby meetings, making it impossible to know who exactly is in the room or which specific policy options are discussed."
Commenting on the findings, CEO's transparency campaigner Vicky Cann said, "Brexit will strongly affect people's private and professional lives in the UK, so it is vital that the process is as transparent as possible and that many different interests are consulted.
"But we observe a strong corporate bias in the lobby meetings of both the UK and the EU Brexit negotiators. Civil society groups and SMEs have had far fewer opportunities to voice their needs, concerns, and proposals around Brexit."
Further comment comes from Jean Blaylock, a campaigner at Global Justice Now, who said, "The corporate bias that has been exposed in this list of meetings shows that we are veering dangerously towards a 'big business Brexit' rather than a Brexit that might take into account the wider needs of UK society."
She said, "Unless there is some sense of transparency and accountability in this process, there is every chance that the UK government will use Brexit as an opportunity to do away will all manner of vital protections relating to labour rights, consumer standards and the environment."