I picked up our free cups of tea and biscuits and carried them across the café towards my Mum. I'd chosen that particular table because it was near the loo. And it had to be a table rather than comfy sofas because if she got down into one of those, I knew we'd make a spectacle of ourselves getting her back up again.

She was rummaging around in her handbag for a hanky, lipstick, glasses, who knows what.

‘Have you got your hearing aid in?' I bellowed.

‘No need to shout,' she said testily. ‘Yes of course.' Then smiling again: ‘Oooh nice cuppa tea.'

It was pensioner's discount showing of ‘Brokeback Mountain' at my local cinema. Mum was in fine spirits and determined to enjoy every moment of her afternoon out. Perching her glasses on the end of her nose, she took a sip of tea and surveyed the café with pale grey eyes.

There were many other stooping backs and wrinkled faces around. Mainly in pairs. Mum nudged me.

‘Look,' she said in a loud stage whisper, raising her eyebrows towards two women. They were a little younger than her, taller (not difficult when you are 4'10" and shrinking), rather elegant and....clearly a couple.

‘Shhhh,' I hissed, mortified. Mum's deafness meant her days of quiet communication were long gone. I feared what she would say next - stating the bleeding obvious was her forte. But she remained quiet, took another sip, then tapped my arm and gestured towards two men, raising her eyebrows again and giving me a big grin. It suddenly occurred to me she had a point. The café was full of same-sex couples who, in their youth, would have thought an afternoon out at the cinema together, holding hands, feeling relaxed, was the stuff of dreams.

Mum was entranced. She loved people who didn't tread the conventional path. To anyone who passed her as she stacked ready meals and mint humbugs into her supermarket trolley, she would have seemed to be the archetypal widow in her 70's; fingers bent with arthritis, eyesight too far gone to spot the forgotten smear of breakfast on her sensible polo neck jumper. But within her lay the heart of a rebel.

She had, after all, had an affair with my father for 14 years before he finally left his (second) wife. While she waited for him, she'd managed to notch up a substantial career as a fashion illustrator. And from the time she drew Quentin Crisp when he was a model at her art school, she took great delight in her gay friends from London's fashion industry.

After she'd moved to suburbia with Dad, they reinvented themselves as the perfect 50's couple, leaving all traces of scandal behind. Dad hated any reminder, but Mum's sense of mischief couldn't help itself. How she'd crowed when Charles eventually married Camilla, delighting in the ruffled feathers of the more staid ladies with whom she now shared her retirement flat complex.

Taking my elderly mother to see a film about a love affair between two men was entirely normal in my family. A pensioner's discount and free biscuits made it all the better.

And so ‘Brokeback Mountain' unfolded, set against vast Wyoming skies and landscapes, a tale of two cowboys, Ennis (Heath Ledger) and Jack (Jake Gyllenhaal), who shock themselves by falling in love. Ennis is haunted by the memory of the murder of a gay man during his childhood and so resists all attempts by Jack to spend their lives together. So Jack gets married, although they continue to meet and to love each other and to wrestle with the norms of society until another tragedy befalls them and they are parted forever.

I cried pretty much throughout the whole film, for reasons of my own lost loves. And whenever I see it now, I cry even more, as Mum is no longer with me and the absence of that love in my life is the greatest loss of all.

I snuffled into my tissues at the end, and as I loaded myself up with her handbag and walking stick in preparation to manoeuvre her out, she gave her verdict.

‘Well, I enjoyed that love, thanks for taking me. But I really don't understand why they couldn't be together.'

Clearly all our preparations had failed. The crucial explanatory scenes had somehow not got past either her cataracts or her worn out ear drums. But never mind. For those few hours we'd had some fun together. And it had reminded me that forbidden love, of whatever variety, is nothing new.