Image copyright Getty Images

Online fashion giant Asos has changed its returns policy.

It is lengthening the time allowed for returns of unwanted items, but is threatening to investigate and "take action" if it notices anything unusual.

It says if it suspects someone is actually wearing and returning goods or ordering and returning "loads", it might deactivate the account.

Late last year, the company, the biggest online retailer in the UK, warned profits growth was slowing.

Asos stocks more than 850 brands and ships all over the world.

It said in November that "unprecedented" discounting had hit its trading, adding that cutting prices to match rivals had not shifted more clothes.

Online shoppers tend to overorder as a rule because size and fit differs between brands and they have the time and space to experiment with potential purchases in their homes.

The BBC spoke last year to a shopper who regularly ordered £400 worth of clothes and generally returned half of them.

Adding to the returns pile is the "snap and send back" trend, whereby customers post pictures on social media of themselves in new outfits.

Image copyright Asos

Certain users do not like being seen in the same outfit twice, making it tempting to use an outfit once and return it.

The company's note to customers, sent this week, states: "If we notice an unusual pattern of returns activity that doesn't sit right: eg we suspect someone is actually wearing their purchases and then returning them or ordering and returning loads - way, waaay more than even the most loyal Asos customer would order - then we might have to deactivate the account and any associated accounts.

"If this happens to you and you think we've made a mistake, please get in touch with customer care and we'll be happy to discuss it with you.

"We also need to make sure our returns remain sustainable for us and for the environment, so if we notice an unusual pattern, we might investigate and take action.

"It's unlikely to affect you, but we wanted to give you a heads up (more deets below). Thanks for being a great Asos shopper!"