Red and white colours of title winners Cliftonville joined by LGBT rainbow banner flown by gay supporters at their home stadium as well as other grounds across Northern Ireland

The newly crowned Irish League champions Cliftonville may have secured unprecedented back-to-back titles this weekend but a section of the north Belfast side's support have also made their own history this season: the club's gay fans and those who stand in solidarity with them.

Their main colours are Cliftonville's red and white but the supporters have also raised the LGBT rainbow banner both at their Solitude stadium home as well as other grounds across the region.

In response to unionist politicians at Stormont blocking gay marriage equality in Northern Ireland and to highlight general homophobia, fans, gay and straight, flew the flag throughout the season.

Before lifting the Irish League trophy, the Gibson Cup, on Saturday in their last match of the season against north Belfast rivals Crusaders, the supporters said they hoped their example will allow other LGBT football fans to feel more comfortable at grounds across these islands.

Pedro Donald, a gay Cliftvonville fan from south Belfast, said he had wondered all season why the rainbow one was there alongside the other banners. The 48-year-old said: "It sums up a lot of what is happening at Cliftonville. People are being more forward thinking, being more 21st century, being more current. Which in general is what football needs across these islands because the attitude here is still backward in regards to sexuality or race or gender.

"It used to be said in English football that it was more 'men only' even than the British Army. So Cliftonville have led the way and that is great. When I saw the flag I was surprised because it looks out of place at the stadium. But I think most people don't bat an eyelid it's there, which is great.

"It has sent a signal to the gay community that you are welcome here. I have a rainbow flag in the Sunflower Bar, which is not a gay pub but it is there to make our place more welcoming. So, it's fantastic that the emblem is also up at Solitude."

Arthur Magee, a life-long Cliftonville and co-author of The Little Book of Belfast, said the rainbow flag's appearance demonstrated "a club that is inclusive and forward-thinking that is open to all".

Magee, whose tour guide business in the city was badly damaged by the loyalist union flag protests, said it was ironic that "the raising of another flag in this city shows that all colours and creeds are welcome at Solitude".

Brian Smyth told the Guardian he and his fellow fans came up with the idea of flying the rainbow flag of the global gay rights movement, albeit with the Cliftonville shamrock crest stencilled on to the middle of the banner, in opposition to homophobia both inside and outside the game.

"The idea came about after the failure of Stormont to pass the Marriage Equality Act last year and the anger felt by a number of us. The idea was initially discussed after our Champions League game in Glasgow [against Celtic] last July, and how football was one of the last bastions of homophobia, especially in the North.

"Lots of young men attend Irish league games, no doubt just like wider society, some may be struggling to come to terms with their sexuality and being safely able to open up, it is seen as a visual symbol of support to our friends in the LGBT community," he said.

The 39-year-old north Belfast native said: "Those involved ranged from the unofficial Cliftonville podcast of which I am a part, to about a dozen other lads aged from early 20s up, who back the initial idea and put the money towards the making of the banner.

"Are there gay Cliftonville fans? Undoubtedly yes, just as there are gay fans of other clubs."

Smyth said their flag has been welcomed by fellow supporters and was even on display on Easter Tuesday at Portadown's Shamrock Park where Cliftonville won 2-0 to confirm their second championship in a row – the first ever consecutive title run in the history of Ireland's oldest football club.

"Cliftonville fans have been fully supportive; contrary to certain opinion, the vast majority of our support are very tolerant and laid back," he said.

As for the supporters of other clubs including their fiercest rivals and main challengers this season, Linfield, Smyth said most of them back their initiative and he was not surprised there was so much solidarity with their cause.

"There have been some comments on different forms of social media from fans of other clubs, but at the same time we have had support from other elements within those clubs. It's not fair to tar one club, due to a few morons who can barely think for themselves.

"I've had Linfield fans support what we have done, which gives you a degree of hope of where we are going, despite the actions of some political representatives around issues such as marriage equality and tackling homophobia."

Smyth said he was proud his group among the wider Cliftonville support were also making history. "I think we are the first club North or South on this island, I haven't heard any other clubs do something similar. As for across the water, I think Bradford City openly fly one, I'm unsure of others. I regularly travel to Germany to watch Hertha Berlin and they are on display inside the Olympic Stadium, and they have an active LGBT supporters' club.

"I think we are witnessing a gradual change and homophobia being challenged with football, not only locally but on these two islands, it's a long battle, just like sectarianism, which the local game has made massive strides in tackling over the past decade," he added.