Media playback is unsupported on your device Media caption Jacob and Charlotte: "We haven't had sex in three years"

Some 18% of respondents under the age of 30 have had sex fewer than 10 times in the past year, a survey of 2,000 people on websites Mumsnet and Gransnet has found. Among all ages, the figure was 29%. We meet three couples who, while madly in love, fall into this category.

"Our lack of sex life at the moment is down to me," Amanda, 35, tells the BBC's Victoria Derbyshire programme.

"I'm so tired all the time because my job is full on and it's full on at home. It's like my libido is tired."

Amanda and Steve have been married for six years.

Watching their 22-month-old son, Elliott, happily marching around the room, they laugh to one another as they explain why they now have sex about once every six weeks.

"Daytime sex and afternoon sex - with a kid around that's not happening," says Steve, from London.

"Even if you put him down for a nap for two hours, you're just kind of like, 'I should probably do other stuff or catch up on some sleep.'"

But it is not just parents having less satisfying sex lives, according to counsellor and sex therapist Martin Burrow, from the organisation Relate.

Image caption Amanda and Steve struggle to find the time and energy to have sex

"We certainly seem to be seeing more people reporting that they are dissatisfied in their sexual relationship," he says.

"Whether that's a cultural shift in people being more comfortable to talk about sex or whether people are having less sex, I'm not sure.

"You can have a successful relationship whether there is sex in it or not.

"Some people don't need to have sex to be happy - some people do."

Jacob and Charlotte, both 23, are very much in love - but sex is not part of their relationship.

"We've been together for four years. We haven't had sex for the last three of them - and we're not planning to," Charlotte says.

She is asexual, though Jacob is not.

"We sort of tried [having sex] to see what worked for the first six months. It really wasn't making either of us happy.

"Jacob doesn't want to be having sex with someone who doesn't want to be having sex."

For some men, this might have been a deal-breaker - but not for Jacob.

"I have a fantastic relationship with a wonderful person," he says. "There are other ways to show affection."

Others, however, are not always as understanding.

Charlotte says: "I don't think I can have a conversation with someone about it without it being implied [not having sex is a] burden that's been put on me, when actually it's a choice I've made.

"It's really sad how some people prioritise sex over happiness."

Image caption Steve and Thom, who are married, have never had sex

Thom and Steve, from Bristol, have been together for four years, and got married last year. They have never had sex with each other.

Both identify as asexual and joke that their first date - when they ended up sleeping next to one another - was "one of the best one-night stands we've both had where nothing has happened".

Thom believes society is becoming increasingly sexualised but this is "not reflective of people having more sex".

Although he adds: "There's more pressure to have sex and maybe people are forcing themselves to have more regular sex".

The couple say people are shocked when they say they have never had sex, and often ask how they can love each other without it.

The reply they give is simple: "You can have sex without the love, so why can't love without sex exist?"

Image caption Dr Martin Burrow says couples can be intimate without having sex

For Martin, when it comes to the amount of sex in relationships, "normal doesn't exist".

Some couples, he says, can "reach high levels of intimacy without having sex".

For others, the amount of sex they have will often ebb and flow, affected by things such as having young children, work, fatigue and illness.

Amanda says communication between her and Steve has been the key to having a healthy and strong relationship without regular sex.

"Don't be too disheartened," she advises new parents in a similar position, "because it happens to all of us."

She laughs as she turns to Steve and says: "We will get it back. I promise."

Watch the BBC's Victoria Derbyshire programme on weekdays between 09:00 and 11:00 BST on BBC Two and the BBC News channel in the UK and on iPlayer afterwards.