The overall picture is complicated. National Agencies / NGOs may gain central funding to deliver a particular service, eg home adaptations, and then partner with a local organisation to deliver that service.
MyAgeingParent.com
https://www.informationnow.org.uk/organisation/my-ageing-parent/
https://www.facebook.com/myageingparent/
https://twitter.com/myageingparent?lang=en
When they get older:- http://www.whentheygetolder.co.uk/
First Stop care Advice: http://www.firststopcareadvice.org.uk/
Age Action Alliance: http://ageactionalliance.org/