The Conservative party allegedly operated a secret call centre during the election campaign that may have broken data protection and election laws, according to an investigation by Channel 4 News.

An undercover investigation by the programme has found that the party used a market research firm to make thousands of cold calls to voters in marginal seats in the weeks before the election.

Call centre employees working on behalf of the party used a script that appeared to canvass for support rather than conduct market research. On the day of the election, call centre employees contacted voters to promote individual candidates, which may be a breach of electoral law, the investigation claimed.

At the start of the election campaign, the information commissioner, Elizabeth Denham, wrote to all the major political parties reminding them of the law around telephone calls and data protection. She said that calling voters to promote a political party was “direct marketing” and was regulated by law.

The government also announced during the campaign that it wanted to tighten up the laws on nuisance calls and a bill on the issue was included in the Queen’s speech.

The Channel 4 News investigation, which ran over several weeks, found that a team employed by the Conservatives rang voters from a call centre in Neath, south Wales.

Operating from a script, the staff carried out calls for “market research” and “polling”. Identifying likely Tory voters in marginal seats could be important for the get-out-the-vote operation on election day, and also enable a political party to better direct its canvassing operation.

On election day, undecided voters were told that “the election result in your marginal constituency is going to be very close between Theresa May’s Conservatives and Jeremy Corbyn’s Labour party”.

They were then asked: “So does knowing that you live in a marginal constituency that will determine who is prime minister for the Brexit negotiations, does that make you a lot more likely to vote for Theresa May’s Conservative candidate or a little more likely to vote for Theresa May’s Conservative candidate, or are you still unsure, or does it not make a difference?”

At an earlier stage of the campaign, the call centre staff said they were calling from a company called Axe Research, which does not appear to exist. Under the Data Protection Act, callers must disclose who they are and how the data will be used.

Asked what Axe Research was, one supervisor told Channel 4 News: “It’s just the name we do these surveys under, basically. I did a Google search, nothing comes up. But as far as anyone’s concerned, yeah, we’re a legit independent market research company.”

A week before the election, the same call centre staff started saying they were calling on behalf of Theresa May’s Conservatives.

The Conservative party said the call centre was conducting market research on its behalf, and was not canvassing for votes. The call centre confirmed it was employed by the party, but denied canvassing on its behalf.

A Conservative spokesman said: “Political parties of all colours pay for market research and direct marketing calls. All the scripts supplied by the party for these calls are compliant with data protection and information law.”

Evidence obtained by Channel 4 News suggests that on the day of the election, staff called voters in 10 marginal seats, including Bridgend, Gower, Clwyd South and Wrexham.

According to the Representation of the People Act, it is illegal to employ someone “for payment or promise of payment as a canvasser for the purpose of promoting or procuring a candidate’s election”.

Anya Proops, a QC specialising in information law, said that political parties had to ensure that third parties working on their behalf followed the law: “There are restraints, legal constraints in the Representation of the People Act, around paying people to canvass, to campaign.

“It’s an illegal practice, it’s prohibited under the legislation and in so far as it’s something which has tainted the overall result in favour of a political candidate, then it can void that result.”

She said it also raised concerns over data protection laws: “If you’re going to process my data, I should know who you are and what you’re going to do with my data. These are fundamental tenets of this legislation. And obviously what this means is that if you’ve got a situation where the company that’s calling you is concealing their true identity or is misleading the person who is receiving the call, then that is obviously a problem under the privacy legislation.”

An undercover reporter for Channel 4 was recruited by Blue Telecoms, which is run by Sascha Lopez, a businessman who stood as a local council candidate for the Tories in the 2017 local elections.

Lopez said: “In relation to the Conservative party project, I am unable to comment on the content of the scripts or calls to TPS [Telephone Preference Service] numbers, as the scripts and lists of who to call and when to call were given to us by Conservative campaign HQ in London and were not influenced by my team. However I can advise we were engaged to conduct market research and polling for the Conservative party, and at no time were we engaged to conduct any form of marketing or canvassing by the party or its candidates.” He also said they followed the regulations given by the Telephone Preference Service.

Lopez said that Blue Telecoms and Axe Research are “trading styles” of the Lopez Group.