Some believe hedgehogs have been declining since the 1960s.

Hedgehog numbers have been dwindling in recent years and have fallen by 20% since 2001.

The People's Trust for Endangered Species wants the public to take part in the UK-wide Hogwatch survey.

Dr Paul Bright, study co-ordinator, says the creation of a "hedgehog map" will help preserve a garden favourite.

Dr Bright, of Royal Holloway, University of London, said: "It is vital to know where hedgehogs are still present and determine why their numbers appear to be falling."

He said the survey, launched at the start of Hedgehog Awareness Week, was simple to carry out.

Hedgehogs have been around for 20 million years - we want to ensure they will be around in the next century Dr Paul Bright, University of London

"All we're asking is for people to tell us where they saw hedgehogs last year and then we'll go back to them later on this summer to see whether or not they've seen hedgehogs this year," he said

"This will not only help us safeguard an endearing favourite of the British garden but also many other species with similar needs," he said.

Whilst figures show hedgehog numbers have reduced by one fifth since 2001, some experts believe they have been in decline since the 1960s.

The popularity of so-called garden makeovers, including the fashion for decking, is thought to be among the reasons hedgehogs are finding it harder to thrive in urban areas.

Dr Bright added: "Hedgehogs have been around for 20 million years - we want to ensure they will be around in the next century."