More than 120 Conservative MPs, including Jeremy Hunt, Liz Truss, Sajid Javid and Gillian Keegan, paid £100,000 of taxpayers’ money to the Conservatives’ in-house web design services, it can be revealed.

The MPs used the Bluetree website service to design their websites. When billed by Bluetree, they would pay for the sites then claim back the costs from the public purse via expenses, prompting a complaint to parliament’s expenses watchdog about the practice.

Conservative Campaign Headquarters (CCHQ) has denied Bluetree is wholly owned by the party and says it is a separate organisation, but repeatedly refused to deny the party receives income from the company, saying it has “commercial arrangements with CCHQ”.

The Independent Parliamentary Standards Authority (Ipsa) has said it would not allow websites to be funded if it was clear they were being used for party political purposes – regardless of the services offered by the company. It said if any evidence was found that rules had been broken then it would work with the MP to make amendments or repay expenses.

Senior transparency campaigners said they were alarmed if MPs were using taxpayer funds that could end up with the Conservative party. Tom Brake, the director of Unlock Democracy, said the money should be repaid if any surveys from the website were used to give MPs information for campaigning.

The party said Bluetree was part of a registered company separate from the Conservative party but would not say what that company was. All contact details for Bluetree on its website are directed to CCHQ and Bluetree does not have a separate Companies House registration.