Police say they are carrying out an investigation of “scale and significance” into allegations the Conservative Party broke the law during the election campaign with its use of a call centre in Wales.

The investigation into the contracting of the business in Neath was confirmed in a letter from South Wales Police to Labour MP Wayne David.

Secret footage obtained by Channel 4 News suggested the Tories may have broken data protection and election laws by using Blue Telecoms to directly contact voters in marginal seats.

The Conservative Party has said it did not break the law by using the company, which it said was hired to carry out legal market research and direct marketing.

In a letter to Mr David, South Wales Police confirmed the investigation is being carried out by its economic crime unit, who have experience in dealing with “electoral integrity investigations”.

It adds there is no timescale for the investigation because it is of “sufficient scale and significance that South Wales Police are unable to offer any specific timescale”.

“Rest assured that the officers within this department have the required specialist skills and expertise for this often challenging area of business and will, as with all investigations, act in a diligent and expeditious manner,” the letter said.

The Information Commissioner’s Office also confirmed it is “currently investigating the Conservative Party in relation to a possible breach of Regulation 21 of the Privacy and Electronic Communications Regulations 2003”.

Mr David, Labour MP for Caerphilly, said: “I am pleased that both the police and the Information Commissioner’s Office are conducting detailed investigations.

“The allegations that the Conservative Party and Blue Telecoms broke electoral law during a general election campaign are extremely serious and the public need to have confidence in our electoral process. That is fundamental to our democracy.”

A spokesman for South Wales Police said: “South Wales Police is currently reviewing information received in regards to Blue Telecoms.

“It would be inappropriate to comment further at this time.”

A Conservative spokesman said: “We are unable to comment on an ongoing investigation.”