Alexander Nix, the former chief executive of the elections consultancy Cambridge Analytica, is facing fresh questions about his conduct after a leak of documents revealed he used a highly offensive racial slur to describe the prime minister of Barbados.

The British consultant, who lost his business after an investigation by the Observer exposed the firm’s unauthorised use of data from millions of Facebook users, has been pitching to once again run election campaigns in the Caribbean.

Nix had worked in the region previously for SCL Elections, a sister company of Cambridge Analytica, before both closed down earlier this year.

New details around the firm’s work in the Caribbean – and the tactics it was prepared to use – have emerged from leaked emails and documents relating to SCL.

The Guardian has seen an exchange of messages in which Nix appears to refer to Mia Mottley, who was elected prime minister of Barbados in May, and senator Lucille Moe, who is the country’s information minister, as “niggers”. The messages are dated October 2010.

At the time, it appears SCL was pitching for business with the Barbados Labour party and had apparently attempted to make contact with Moe and Mottley, who was then leader of the opposition.

A member of SCL’s team wrote to Nix on 15 October, saying: “I get the distinct impression they don’t want to talk to us.” To which the SCL Elections boss replied: “they just niggers.”

The Guardian asked Nix about the exchange. He did not respond to a request for comment. He has previously blamed the “global liberal media” for bringing down Cambridge Analytica.

In an emailed statement, Moe confirmed that SCL had contacted the Barbados Labour party in order to offer its services. She said: “We were not comfortable working with them so we took a decision not to engage their services.”

The disclosure is likely to fuel concerns about a return by Nix to the region, where his work was the subject of controversy and denunciations from local politicians long before SCL and Cambridge Analytica came under scrutiny in Britain.

Last month, the Guardian has been told, Nix made contact with the opposition party of St Kitts and Nevis, a state in the eastern Caribbean.

According to a senior source from the Saint Kitts and Nevis Labour party, Nix offered to manage its next campaign. A general election is expected to be called in the coming months, with opposition leader Denzil Douglas hoping to oust the prime minister.

“Nix said although the company has been changed, the people who work there are the same and so they were available to provide services in campaign management,” the source claimed. The offer has not been accepted by the party.

Nix did not, apparently, give the name of his new firm. Since Cambridge Analytica went into administration in May, a number of reports have surfaced of former staff and directors regrouping at new businesses. One former executive, Mark Turnbull, is now managing director of Auspex International, a company launched in July that bills itself as an “ethically based” geopolitical consultancy. Nix has not declared any involvement with Auspex.

SCL and Cambridge Analytica claimed to have advised political parties in more than 100 elections, spanning 30 countries – many of them former British colonies.

Both companies were forced to close following revelations about the behaviour of Cambridge Analytica – and the new leak highlights the array of dirty tricks SCL was prepared to deploy during the Caribbean campaigns.

During the 2010 election in Dominica, for instance, staff pretended to be anthropology researchers from a fictitious London university, complete with a fake logo. As part of its pitch for a campaign in St Lucia the same year, SCL offered to create an NGO from scratch to praise and endorse the party it was working for.

SCL explained that the NGO would organise “events that are bi-partisan in nature (or appear to be)”, “raise issues of interest to the client” and “investigate opposition allegations and neutralize attacks”. The service would cost $20,000 (£15,000) a month.

In addition, SCL proposed carrying out a sting against a rival, who was to be contacted by someone from the firm posing as a representative of a European construction group interested in winning business on the island – in return for a donation to his party.

In the event, no St Lucian election was held that year. The plans were not, therefore, put into effect and there is no suggestion local politicians were informed of or approved these tactics.

SCL worked for the St Kitts Labour party in two previous elections. The first was in 2010, when the firm helped Douglas secure a fourth term as prime minister. His 20-year premiership was eventually brought to an end in 2015 when Labour was once again advised by SCL. His successor, Timothy Harris, is expected to call the next general election later this year or early in 2019.

Additional reporting by Stephanie Kirchgaessner.

