The Guardian and the Observer have received complaints that agreements for car hire from rentmac.co.uk, a car hire firm that has recently advertised in several newspapers, have not been honoured.

Readers have raised concerns about the company, which has advertised in the Guardian. They are particularly anxious about the fact it asks for payment through direct bank transfer. One reader said he had paid a £500 deposit into a bank account, but had not heard back from the company or received the car he had been promised. Another said he had lost £320.

A Guardian spokesperson said: "We have been made aware of complaints that agreements for car hire from rentmac.co.uk, booked in response to advertisements published in the national press, including in the Guardian, have not been honoured. The matter is being investigated and in the meantime we can confirm that we have no further advertisements from rentmac.co.uk scheduled to run in the paper."

A Guardian reporter contacted rentmac.co.uk today and was told that Terence Smith, described by colleagues as the "director and main shareholder" of the company, was in the Caribbean.

Gary Smith, a customer services manager, said rentmac.co.uk had been unable to deliver cars to some customers, but said this was because of problems with the weather.

He said the company was experiencing a backlog and between 30 and 40 customers had not received cars over the last fortnight. Delivery of vehicles from Scotland that would have swelled its fleet "never actually arrived" owing to the weather, he said. "We found ourselves in a situation where we had actually overbooked," he said."We do hope that we will be up to date in the new year."