Thousands of online shoppers have been warned they may not receive their goods by Christmas after snow crippled some deliveries.

Royal Mail said it is doing "everything possible" to ensure the post arrives on time.

But it said the "severe weather and road conditions" means reaching some addresses is not possible.

"More than 95% of Royal Mail's operation is working completely normally but, in a very small number of areas, some deliveries have been subject to disruption as the severe weather and road conditions mean that we cannot get to some addresses safely," said a Royal Mail spokeswoman.

"We are keeping the mail moving and doing everything possible to deliver all letters and parcels by the latest recommended posting dates for Christmas."

Meanwhile, a spokeswoman for supermarket chain Asda said some deliveries had been cancelled because of the conditions.

"Clearly the weather has led to issues in a small number of cases," she said.

"We are doing everything we can to get deliveries to people."

She said deliveries would continue into Christmas Eve.

© Press Association 2009