A beginning:

Societies
The Vegan Society https://www.vegansociety.com
The Vegetarian Society https://www.vegsoc.org/

Campaigning sites
People for the Ethical Treatment of Animals www.peta.org.uk
Compassion in World Farming http://www.ciwf.org.uk/
Free From Harm (and possibly the best article on veganism ever): http://freefromharm.org/why-vegan/

COVID-19: Why going vegan might help prevent a future pandemic: https://www.thevegankind.com/news/2020-05-22-uk-doctors-say-going-vegan-will-help-prevent-future-pandemic?mc_cid=ab5365fca0&mc_eid=cf047ed018

This one gives you, at the bottom of the home page, the numbers of exactly how many animals have been killed for food in the seconds it takes you to scroll to the bottom of the page. ‘Shocking’ doesn’t start to go there. It’s numbing. Read this guy’s books (see ‘Resources’). http://www.abolitionistapproach.com/about/gary-l-francione/#.V34-0Y5byC4

Further info (inc. the environmental aspects, with references & stats)
http://www.veganfuturenow.com/answering-the-objections-to-veganism/#its-the-circle-of-life  those tricky sticky questions non-vegans will raise, & how to respond
The World Peace Diet http://www.worldpeacediet.com/
http://www.veganuary.com/about/
http://www.howdoigovegan.com
http://www.theguardian.com/environment/2010/jun/02/un-report-meat-free-diet
http://www.onegreenplanet.org

George Monbiot’s website has a number of informed articles on aspects – and the costs – of meat-eating. Monbiot himself was a vegan, then wasn’t, but is again (see below) as he now feels it’s the only sustainable way forward. His focus is on land use and climate change.
http://www.monbiot.com/2015/11/19/pregnant-silence/
https://www.theguardian.com/commentisfree/2016/aug/09/vegan-corrupt-food-system-meat-dairy (George Monbiot is now a vegan. Here’s why)
https://www.monbiot.com/2016/08/11/stock-answer/
https://www.monbiot.com/2018/01/31/stepping-back-from-the-brink/
https://www.monbiot.com/2018/06/13/butchery-of-the-planet/

Climate emergency
https://freefromharm.org/agriculture-environment/plant-based-climate/

The protein myth
https://humaneherald.org/2019/05/09/comparison-of-protein-and-caloric-energy-kcal-produced-per-acre-on-u-s-farms/

https://www.theguardian.com/commentisfree/2016/jul/19/parents-raising-vegan-babies (bringing up the vegan child)
http://vegetariancalculator.com/ this link will calculate for you how many animals’ lives you’ve saved by not eating them, and how many pounds of C02 you haven’t released into the atmosphere… Read and feel proud!
http://www.riverford.co.uk/tor/how-much-meat the organic veg-box company Riverford also provide organic meat. However, they are campaigning to cut our meat consumption

Buddhism and the vegan (Thich Nhat Hanh)
http://www.onegreenplanet.org/environment/thich-nhat-hanh-leader-draws-attention-to-food-choices-and-planet/?utm_source=Green+Monster+Mailing+List&utm_campaign=c02480276b-NEWSLETTER_EMAIL_CAMPAIGN&utm_medium=email&utm_term=0_bbf62ddf34-c02480276b-106931317

Nutritional info
http://www.veganhealth.org
https://www.theveganrd.com/  Full of excellent info
http://www.nhs.uk/Livewell/Vegetarianhealth/Pages/Vegandiets.aspx
(also http://www.nhs.uk/Livewell/Vegetarianhealth/Pages/david-scott.aspx) http://www.theveganrd.com/food-guide-for-vegans
http://jacknorrisrd.com/response-to-not-soy-fast/
(information on the controversy about soy)
https://plantbasedhealthprofessionals.com UK info, courses, recipes etc
http://www.pcrm.org/health/diets/success-story
(has some stories about people’s improving health on a vegan diet, and some info re vegan nutrition on the site)

Recipes
http://www.onegreenplanet.org
truly wonderful recipes, and info
http://ohsheglows.com
(fabulous recipes)
http://www.unconventionalbaker.com/recipes
her vegan tiramisu is a dream…

Sourcing stuff
http://www.ethicalsuperstore.com
Sourcing vegan/eco stuff that’s hard to find locally
https://www.thevegankindsupermarket.com
You might also be interested in http://www.tolhurstorganic.co.uk/
and https://hodmedods.co.uk/ (protein-rich beans, lentils other pulses grown in GB)

Clothing
http://www.eco-vegan-shoes.com/
https://www.greenshoes.co.uk/  Once, back in the day, I was a shoemaker. These people were friends, and they continue with their shoes and their ethical policies. You can buy vegan made-to-measure shoes here.

Vegan places to stay
In the Northumbrian border with Scotland: http://www.loafbnb.co.uk/

And have a look at this link; here’s the son of a British farmer sending an unlikely message (for someone in such a position):
https://www.facebook.com/gary.yourofsky/videos/948899375165311/?fref=nf

Another video:
https://youtu.be/7eoF6w7R9oI