Parents in Edinburgh have complained to the advertising watchdog after posters for an adult-themed film were plastered across buses in the city.

The Advertising Standards Authority (ASA) allowed the posters for 18-rated film, Zack and Miri Make a Porno, to be put on the buses despite the fact that their own email firewall system blocked the word “porno” when parents complained.

One mother, Andrea Becquemont, described how her eight-year-old daughter asked her what the word meant.

“I just said it’s a silly word they use for adult movies. I couldn’t think of anything else to say.”

She added: “If it is acceptable, why won’t the council accept an email which contains the word porno, and why is bleeped out on the radio during the day?

“Children shouldn’t be asking their mum or dad what does porno mean? It’s too much.”

A spokesman for the bus company that ran the ads said it believed they conformed to the British Code of Advertising, and stressed that they had been approved by the ASA and the Committee of Advertising Practice.

However, the posters were removed from the buses after the ASA received 149 complaints.