A successful TV double act is like a happy marriage, and that’s what it feels like to hang out with former Great British Bake Off presenters Mel Giedroyc and Sue Perkins.

The closeness and affection between them is clear – they even have pet names for each other – Mel is ‘Melly’ and Sue is ‘Perks,’ – and they’re on such a similar wavelength they finish each other’s sentences.

They have been a comedy duo since meeting as students at Cambridge in 1988, and had huge success since the 1990s, when they shot to fame in French and Saunders’ sketch show. They’ve remained the best of friends for decades, Sue says they’ve only had one argument, but neither can remember what it was about.

‘It’s such a precious relationship,’ says Mel, 51. ‘It’s so valuable, what we have and the fact that we’ve been friends for 30 years. I’m getting emotional! It’s rooted in a real friendship, so if anything went wrong, it would just be so devastating.’

Sue says that being together through their 20s and 30s forged a strong bond between them. ‘A row would be so catastrophic to our family and friends’ ecosystem that I can’t imagine it,’ says Sue, 50.

However, she jokes that it could get tricky when they both go through the menopause.

‘Let’s say I was to go through a devastating menopause and there’s a shimmering, tensile, low-oestrogen vibe going on – we could just rip each other’s faces off. We’re just a little bit off that yet, but we’ll have to be quite careful.’ Mel interjects, ‘This is like a therapy session!’ They both collapse laughing.

The pair have done several solo projects – Mel had presenting jobs on the TV talent search Let it Shine and the game show Letterbox, while Sue has made documentaries on Japan and the river Ganges, as well as the quiz show Insert Name Here.

Both are in settled romantic relationships – Mel has been married to TV director Ben Morris for 17 years and they have two daughters, while Sue’s partner since 2014 is Naked Attraction presenter Anna Richardson.

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But the old friends are never out of contact for long. ‘We can go for a week or two and not speak, but then we’ll talk and it will be obsessive for a while,’ says Sue.

‘There will be flurries of quite intense messaging. Usually it’s when I’ll hear a song or see an image and it takes me back. We’re always in each other’s orbit.’

They’re thrilled to be back working together, particularly on a project that injects drama into their double act. In the new sitcom Hitmen, they play Fran (Sue) and Jamie (Mel) – professional assassins who are hopeless in their personal lives.

‘When we did Bake Off it was brilliant,’ says Mel. ‘I just used to look forward to those 10 weeks so much because obviously it was great fun doing the show, but just being able to hang out with Sue was so much fun. And doing this, we spent six weeks together on a daily basis.’

Sue chimes in, ‘We got up super early and I’d just jump out of bed, rushing to it every morning because it’s playtime. It was heaven.’

But acting didn’t come easy to Mel and Sue, who admit that it was a lot harder than presenting. ‘It’s such a learning curve. You present programmes and – don’t tell anyone – it’s quite easy. So this acting lark has been an interesting new challenge,’ concludes Sue.

Hitmen features the high stakes of death and murder and revenge, yet at its centre is a solid friendship, just like Mel and Sue’s.