He is one the world's best guitarists, he's written some of the most memorable rock anthems of all time, and his band Queen is a global phenomenon. But it's not music he wants to be remembered for – it's badgers

When Queen performed at the closing ceremony of the Olympics – Freddie Mercury, towering over the crowd in canary-yellow jacket, leading a call-and-response from beyond the grave, Brian May, crowned in his wonky halo of grey curls, squalling his way through the guitar solo from Brighton Rock, and drummer Roger Taylor, with guest Jessie J, thundering into a rendition of We Will Rock You – they did what they always managed to do so spectacularly live: unite a stadium in belting out an anthem.

They – well May – also managed to do something new: infuriate a significant percentage of the populace. The trouble was his outfit: a characteristic combination of dark trousers, trainers and long frock coat, except from one sleeve peered the head of a fox; from the other, the black and white snout of a badger.

"He's politicising the Olympics!" came the cry, from those who made the connection between his attire and his campaign against the government's then imminent approval of pilot badger culls in Gloucester and Somerset. "To the farmers struggling against bovine TB and fox predation," harrumphed the Countryside Alliance, "a millionaire rock star using a global sporting celebration to undermine their way of life really stuck in the craw." A spokesperson for May said his jacket was in keeping with Danny Boyle's Isles of Wonder theme, including, as it did, a hedgehog, a buzzard, two herons and an adder, "most of which are protected or in decline" – which was plausible, up to a point.

For it is true that May is on a mission. "All the available scientific evidence points to the fact that the cull probably will not work," he says now, sitting in a hotel bar in Kensington. "It will not save a single cow. It might do, but it's a huge unknown – a huge extrapolation, and extrapolation of scientific evidence is a very dangerous game." His voice is soft, languid in the way of someone accustomed to being listened to. "If you talk to any expert on cows and bovine TB in Britain, bar a couple who work for Defra [Department for Environment, Food and Rural Affairs], you will get the same answer, including from Lord Krebs." Krebs led the only major scientific trial of culling, a £50m study known as the randomised badger culling or Krebs trial, which culled 11,000 badgers over five years and found that if certain conditions were met, culling could reduce disease incidence by an average of just 16% over nine years. "Krebs said culling is a crazy idea, we shouldn't be doing it, we should be vaccinating," adds May. "So I'm not a lone voice. I'm not a renegade hippy."

On Friday afternoon, a petition he has launched with Team Badger, a coalition of various animal rights groups, had more than 134,000 signatures, well in excess of the 100,000 required to get a debate considered in parliament. (The coalition includes May's own anti-animal cruelty organisation, established when he realised, in 2010, that David Cameron would try to repeal the anti-hunting act. It is called, with the unapologetic sentimentality that imbues the songs he wrote for Queen, Save Me, and marked the end of his life-long support for the Tory party.)

May is working on the campaign around the clock, talking to scientists, emailing activists, doing interviews, updating his website. "It's threatening my life, it's utterly consuming my life. It makes it difficult to continue a proper family life, it makes it difficult to continue music, to continue astronomy, to continue my stereoscopic adventures." May is, famously, unusual in the rock firmament in that he possesses a PhD in astronomy, and has written books about it (the most recent, The Cosmic Tourist, written with Patrick Moore and Chris Lintott, will be published next month) and another obsession, stereoscopy. "So I suppose I solve the problem by not sleeping very much." He says his friends, largely, support his campaign, but that his wife, Anita Dobson – though helping with the petition, "has at times made me question whether I should be spending this much time on it".

As we talk, his eye is suddenly caught by a scene behind us, and his voice hardens. "Sorry, excuse me, are you having trouble, Anne?" Anne is Anne Brummer, of Harper Asprey Wildlife Rescue Centre in Surrey, who has rescued thousands of animals over the past 25 years and has released many of them on to his land. A waiter has been trying to explain to Anne that the bar is not yet open. "Who says? Can we talk to your manager please?" The gentle tone is suddenly gone; in its place is the full force of rock star high-handedness.

He turns back to me. "Sorry, I hate people who say things can't be done." His tone is avuncular again, expansive. "It must be in my upbringing." In what way? "Well, my parents thought we were middle class" – his father, who when May was a teenager helped him build the guitar he still uses out of motorbike valve springs, a mahogany fireplace, a bike saddle, and mother-of-pearl buttons from his mother's button box, was an electronics draughtsman in the civil service – "but we were very poor. They had a pride in doing things well. Life is too short for people who don't want to do their job well."

Speaking of jobs, it's understandable, isn't it, if farmers feel that it is all very well for someone in a comfortable position … "I'm not in a comfortable position," interjects May. "This is killing me!" I look for a trace of irony, but it doesn't appear to be there. "Yeah, yeah, yeah. Rock stars shouldn't have anything to say about farming. Well, sorry, it's time to wake up. Farming, like every other industry, including mine, has to be open to change or it dies. … [And] if the price of my glass of milk on the table, or my cheese is the death of possibly hundreds of thousands of badgers, I don't want it. I like me milk, I like me cheese, but the day the first shot is fired by the government against the badgers, I will never drink another drop of milk unless I know it's come from a humane farm."

But that, as even some anti-cull activists admit, is just punishing farmers further. "No, it's not. It's giving people the right to choose who to support."

What is it about him and animals, exactly? Where does this passion come from? "It's a childhood thing, but it's been reinforced by the life I've led. I'm an astronomer." Even when he was touring the world with Queen, May kept up with the academic journals. He has an asteroid named after him, has spent months chasing eclipses from Mexico to Outer Mongolia, and periodically appears on the Sky at Night with his friend Patrick Moore. "For a thousand years the Ptolemaic system was believed all round the world. The system says that the Earth is at the centre of the universe. It turns out not to be true. But this idea that we are the centre of creation lingers on – where is the justification to say we are the central piece of evolution? There is nothing to tell us that whatsoever. So why would we use that to justify our exceedingly bad behaviour?"

In fact, he said, a couple of years ago, that he would rather be remembered for his animal rights work than for music or astronomy. Really? "Yep. I won't be remembered in 1,000 years anyway, but I would like to leave this planet knowing that I did what I could to make it a better place, a more decent place, a more compassionate place."

Having said which, he doesn't seem to find this campaigning lark that fulfilling. "People say: 'Are you enjoying it?' No. I love my music, I love my art. And I'm quite good at it." Rolling Stone last year ranked him as 26th of the 100 best guitarists of all time. "So really I should be making music – I have to have time – because if I lose music from my life, I lose my self."

He is about to embark on a short tour with Kelly Ellis, accompanying her on acoustic guitar and performing by candlelight. "It's almost like a reaction to the music that made Queen famous, though if you look at it some of it's very simple. We Will Rock You is very simple. Millionaire Waltz is highly complex."

It is perhaps instructive – or maybe not – that May wrote We Will Rock You, while Freddie Mercury wrote The Millionaire Waltz: for all his obvious intelligence, there is something of the emotional bludgeon about May and his lyrics: they are obviously wildly effective – in 2006, Queen's Greatest Hits became the best-selling album ever – but relatively uncomplicated (unlike his guitar solos): We Will Rock You. The Show Must Go On. I Want It All.

Musically, he and Mercury dovetailed brilliantly, but did he ever feel overshadowed and resentful of his flamboyantly gifted frontman? "No, we actually pushed him forward. It was me who designed that first cover and put him on [it]. That was my vision of what Queen's image would be. Because Freddie was born to it. Though he was very democratic. People often said, in interviews, 'This is your band' – and he'd say, 'Don't be stupid, darling.'" May's voice alters subtly, suddenly there's another person in the room. "This is a band."

What was it like, performing with Mercury again, albeit in the form of a hologram? "It was nice. I mean, Freddie's with us the whole time, really. Freddie's spirit is very strong and we spent so much of our lives together, I can't imagine a day where I wouldn't refer to him in some way. I'm very comfortable with that now. I wasn't in the beginning." In fact, he was so grief-stricken by the loss of his friend and colleague, which came at about the same time as the breakup of his first marriage and the death of his father, that he slipped into a severe depression. "It was quite a long grieving process, but I'm comfortable with it now. He lived life to the full, he created magnificently, from his soul. He was fearless."

During another period of depression, a suicidal episode, May went to a clinic in Arizona. "They said, 'What is your religion, what is your spirituality?' I said: 'I'm not sure.' And they said: 'Well, we need your spirituality to be a centre for your recovery. And I kind of floundered around for a while and in the end it was looking at the stars that gave that feeling back to me.

"There's a great thing called The Serenity Prayer," he says. "It's taught in all kinds of clinics – it starts off with the word God, but you can say Higher Power – 'God, give me the serenity to accept the things I cannot change, the courage to change the things I can, and the wisdom to know the difference.'"

He delivers the homily as if it is not cross-stitched and stuck up on wall after wall throughout the world. "To me that's incredibly empowering and very often if I get to a sort of trough, that's what I look at. It focuses you on the things which you can change." And he stands up to his full 6ft 2in, plus a good five inches or so of hair, and wanders off to be photographed. From the lapel of his frock coat, a badger winks.

• This article was amended on 3 October 2012. The original said John Deacon had performed with Brian May and Roger Taylor at the Olympic closing ceremony. He did not join them.