The British Hedgehog Preservation Society offers help and advice about poorly hedgehogs, maintains a list of UK rehabilitators and hosts a range of downloadable posters and leaflets: https://www.britishhedgehogs.org.uk/
The People’s Trust for endangered Species works to protect ecosystems and threatened species, including hedgehogs. They have compiled a useful list of summaries of scientific papers about the European hedgehog: https://ptes.org/hedgehog-papers/. You can also download the West-European hedgehog Conservation Strategy https://ptes.org/campaigns/hedgehogs/conservation_strategy_for_hedgehogs/ and the guidance for detecting hedgehogs using footprint tunnels https://ptes.org/get-informed/publications/guidance-leaflets/.
Hedgehog Street https://www.hedgehogstreet.org/ is a campaign bringing together people, gardens and hedgehogs. You can learn all about hedgehogs, sign up to become a hedgehog champion and download the latest State of Britain’s Hedgehogs report https://www.hedgehogstreet.org/about-our-hedgehog-street-campaign/stateof/. You can also add your hedgehog sightings and hedgehog holes to their BIG Hedgehog Map: http://bighedgehogmap.org/.
Suffolk Wildlife Trust is running the Ipswich Hedgehog Project. Mark your hedgehog-friendly garden on their map and become an Ipswich hedgehog champion: http://www.suffolkwildlifetrust.org/IpswichHedgehogs
London Wildlife Trust would like help in finding Urban Urchins across London. You can add sightings to their map, help to survey and sign up to borrow a footprint tunnel: http://www.wildlondon.org.uk/hedgehog
Harper Asprey Wildlife Rescue is working to make Surrey Heath a hedgehog-friendly borough: https://www.harperaspreywildliferescue.co.uk/hedgehog
The Mammal Society advocates science-led conservation. You can find out information about hedgehogs, and often answer questionnaires and support campaigns: http://www.mammal.org.uk/
The Royal Parks https://www.royalparks.org.uk/managing-the-parks/conservation-and-improvement-projects/hedgehogsworks with the Zoological Society of London https://www.zsl.org/, Garden Wildlife Health Project https://www.gardenwildlifehealth.org/, the Central Royal Parks Wildlife Group and Dr Nigel Reeve and Professor John Gurnell to survey the hedgehogs in Regent’s Park, London. You can report a sighting, sign up to be a ‘Hedgehog Hero’ and adopt a hedgehog.
Wildlife Watch is the junior branch of The Wildlife Trusts. You can become a member and get involved in lots of activities. They have a range of free downloadable activity sheets, including making compost, making a footprint trap and making a hedgehog home: http://www.wildlifewatch.org.uk/activity-sheets
Wildcare sells Mammal Society footprint tunnels if you would rather buy than make your own: https://www.wildcareshop.com/tracking-tunnel-1.html
Wildpro is an electronic encyclopaedia and library for wildlife, including lots of information on our West-European hedgehog: http://wildpro.twycrosszoo.org/S/0MInsectivor/Erinaceidae/Erinaceus/Erinaceus_europaeus/Erinaceus_europaeus.htm
Pro Igel, the Association for Integrated Nature Conservation in Germany advocates conservation of the West-European hedgehog and hosts a website packed full of hedgehog information: http://www.pro-igel.de/english/about-us.html