B&Q has been drawn into a row after hiring gardening expert Alan Titchmarsh after some critics argued BBC presenters must be impartial.

Titchmarsh was hired by B&Q to encourage more people to take up gardening, make guest appearances at stores and write leaflets. But he also presents BBC’s Chelsea Flower Show coverage and has signed up to front a new BBC Two series Alan’s Garden Secrets.

BBC presenters are allowed to endorse products provided they “do not undermine the BBC’s impartiality”. However, presenter Diarmuid Gavin was barred from presenting the BBC’s Chelsea coverage because he appeared in an advert for a compost company.

The BBC said Titchmarsh has not broken the rules because there is no conflict of interest and his BBC show has not begun filming. A spokesman told The Telegraph: “Alan is not currently on air. We are very careful to ensure that the work all our presenters do outside the BBC does not conflict with their roles presenting BBC programmes.”

A B&Q spokesman said: “Alan Titchmarsh is not endorsing our products. There is no plan for him to appear in B&Q TV adverts. He is helping to get people gardening.”