No laughing matter - Profile: Dawn French and Lenny Henry

If any of these factors were to blame for the two-page legal notice that was issued last week by law firm Schillings announcing that the couple are to split after 25 years of marriage, they have chosen not to say. But it is certainly true that news of the pair's separation has sparked a palpable sense of sadness among a nation of British telly watchers who have long felt a cosy sense of familiarity and kinship with this celebrity couple. They were a pair who seemed somehow normal and approachable, the type you could sit down and have a cup of tea, a slice of cake and a good old chinwag with.

When the pair first met in 1981 at the Comedy Store in London he was the bigger star, an established presence on TV on BBC1's Three Of A Kind with a sizeable following. She was part of the alternative comedy scene, perfecting her double act with partner-in-crime Jennifer Saunders and struggling to break into the big time.

Following their first night together French, brunette, bubbly and buxom, was terrified that Henry might prefer Saunders to herself, as he had been seeing a "lot of blondes" before they got together, and delayed introducing him to her until she got to know him better. In fact, Henry was somewhat overawed by French – by her confidence, presence, middle-class vowels and boarding school education.

Originally from Anglesey in South Wales, French had been an "airforce brat," moving regularly round the country and brought up in a loving family that was violently shattered when her father committed suicide after suffering years of crippling depression when French was just 19.

Henry too had lost his father at the age of 19 – a year after he had won the New Faces talent contest – but his background could not have been more different. The son of poor Jamaican immigrants, as a child he spoke patois in the family home in Dudley in the West Midlands. "We lived in a house with a hairline crack down the middle of it and a sewer that used to burst every summer," he once said.

That they were a mixed-race couple, at a time in Britain when such relationships were still relatively rare – and an increasingly high profile one – meant that they were later to become the target of racist attacks. Excrement was left on their doorstep, graffiti daubed on their walls and on one occasion a burning rag put through their letterbox. But despite what society may have perceived as difficulties, they embraced their cultural differences wholeheartedly, inadvertently becoming the poster children for mixed-race couples across the country.

French once recalled an early visit to Henry's mother, Winifred, who piled her plate high with steaming, spicy Jamaican food. "If I could get through it, then I was in the family," French said. Needless to say, she did.

They married in 1984, in London and settled into a routine that revolved around work, French, as part of The Comic Strip gang and, starting in 1987, the phenomenally successful French & Saunders. Henry, meanwhile, was working on his self-titled stand-up TV show for the BBC, as well as being the figurehead for charity event Comic Relief. Henry later admitted that there was an element of ships-in-the-night about their relationship during that period.

"Our careers came first and, both being very ambitious, we worked hard, he said. "We pushed ourselves to the brink. I'd come home at midnight and Dawn would arrive at 3am, which made things very difficult."

The pair desperately wanted children, and, after two miscarriages, turned to IVF. It was tough, and it didn't work. "It was something Len and I went through together and which we survived," French said. "It was not easy; it was gruelling."

In 1991, they adopted Billie, a mixed race child, and instantly adored her, although French has confessed that she has not found being a parent easy. "Motherhood has tested me beyond belief," she said, while Henry described being a parent as the most difficult and demanding role he'd ever had.

Never an apologist for her size – she lost weight once, for her wedding, and promptly piled it back on, perhaps because Henry, puzzled by her actions, asked her "Who are you doing this for?" – French launched her own range of clothing for plus-size women and talked happily of family dinners and diets being banned in the household. By the late 1990s she was a major TV star thanks to Richard Curtis's massively successful The Vicar Of Dibley, and while her husband's career was on the wane, she was rarely out of the spotlight.

Henry, meanwhile, was in turmoil. When his mother died in 1998 he slipped into a deep, depressive grief which had a profound effect on his relationship with French. She encouraged him to seek therapy.

Things culminated one night at 10.30pm in 1999 when two journalists arrived on the doorstep to inform French that Henry had been allegedly dallying with another woman, having reportedly spent the night in a York hotel room with a 26-year-old Australian receptionist named Merri Cheyne. The tabloids had a field day (much was made of the fact that Cheyne was slim and blonde) and Henry checked into the Priory a few days later.

Later, French was candid about what happened. "The truth is that everyone rushes in to make moral judgments. It can be quite disabling because other people don't actually know what's happened. Couples need to have their own congress to sort things out. That's what Lenny and I did. We agreed to lay all our cards on the table so nothing shocked us."

The two repaired the damage, and before long were gushing again about how much they loved each other. They bought an enormous house on the cliffs in Cornwall, and Henry went to the Open University, where he graduated with an MA (Hons) in English Literature in 2007. While French's career has recently quietened down, Henry's has climbed, climaxing in a critically acclaimed theatre performance of Othello last year.

The two are on holiday with their daughter, now 18, suggesting that a friendship still exists. Poignantly, French told an interviewer less than 18 months ago that, having spent two years working on their house, , they had created their dream home. "It's heavenly, beyond beautiful." she said. "I don't want to move again."

Whether either member of this much-loved partnership will be able to move on without the other is a question both are likely to be highly reluctant to answer.

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• French lost six stone for her wedding to Henry. The dress, a size 12, had to be taken in twice to accommodate her rapidly-shrinking frame.

Their house has a lot of silverware. French has been nominated for six Bafta Awards and also won a Fellowship Bafta along with Jennifer Saunders, above. Henry has a CBE and last year won the Evening Standard Theatre Awards Outstanding Newcomer award.

French has discussed the relationship's temptations. "Some people have a relationship where everything is completely out and we don't really have a relationship like that. It's kind of grown-up. We are around interesting people and sometimes they are going to be interested in you – and how you behave around that is your business."

The couple's daughter Billie is apparently unimpressed with her parents' jobs. "Billie loves horses, sport and music. Nothing could interest her less than our careers. There's nothing remotely showbizzy about our lives when we're at home."