James Corden grins as he joins Gavin And Stacey co-star Ruth Jones at the BBC as the week countdown to the finale episode begins

James Corden couldn't wipe the smile off his face as he was seen leaving the BBC studios on Thursday morning. 

The actor, 46, was joined by his Gavin And Stacey co-star Ruth Jones as the countdown to the series finale draws ever closer with less than a week to go. 

After celebrating the final episode at the special screening at The Ham Yard Hotel on Wednesday, the duo were back out doing more press ahead of the Christmas Day episode. 

James, who plays Smithy in the sitcom, looked stylish in a checked shirt and smart black winter coat. 

Accessorising the look with a pair of black framed glasses, he completed the ensemble with blue denim jeans and white trainers. 

Meanwhile Ruth, 58, who plays Nessa, appeared makeup free as she wrapped up in a turtleneck grey jumper and fur hooded coat. 

The Christmas special will pick up five years on from Nessa's shock proposal to Smithy, which the duo thought would be the final ever scene of the show. 

The supposed 'last ever' installment will air in a 90-minute special on Christmas Day this year after fans of the show begged for an end to the story. 

And James and Ruth are also set to take over BBC Radio 2 Breakfast show on Monday 23rd December ahead of the final episode.  

It comes after James and Ruth revealed Gavin & Stacey fans will be treated to a lot more Smithy and Nessa in the final episode, musing that their characters' 'messy' relationship is the beating heart of the BBC show.

Appearing on the podcast Table Manners with Jessie and Lennie Ware, the actors and writing partners teased the Christmas special, spilling that fans will find out a lot more about Ruth's character Nessa's past as well as her future with Smithy.

'Nessa has had this unbelievable checkered life and you find out more about that in this special — some really fun bits that we wrote,' James explained.

He mused that the reason fans have taken Smithy and Nessa to their hearts is because 'on TV or films, you very rarely see people that look like Ruth and I fall in love.'

'You just don't. I'd be dropping off a TV to Hugh Grant in Bridget Jones and Ruth's like working on a newsstand when someone buys a newspaper.' 

'What I like about the show is that it's so messy and complicated and they just clearly have fantastic sex. I really enjoy that confidence.'

Ruth added though that in the early days, the writers partners were unsure how to pitch the unique relationship, explaining: 

'The first time they had sex was in the very first episode and I think because we didn't quite know what the show was we were probably being quite sitcom about it.'

'We were there, just the two of us, on that road that had meant so much to us and I just, as Ruth, was looking at my dear friend James and when I said 'I loved you with all my heart' I was saying it to you [James],"  Ruth recalled.

Despite the pair now promising the upcoming special actually is the finale, there's been a flurry of fan speculation that there could be more to come.

James is adamant though that this is it, giving an ominous  warning to viewers as she said: 'It can't carry on. When you'll see it, you'll know.'

The pair aren't saying no to working together again with James promising: 'We don't know if we have another idea in us but I can honestly say that if we didn't attempt to try and even explore the idea of writing together then I'd be so disappointed.'

'I couldn't bear it. I love being in the room with James, it's so fun,' Ruth added.

Strictly Come Dancing gave viewers an early Christmas treat with a world exclusive first look at the Gavin and Stacey Christmas special on Saturday night. 

Set to air on Christmas Day, the new episode will pick up from the dramatic cliffhanger of the 2019 special, which saw Nessa on one knee, proposing to Smithy.

The 2019 episode, which ended with Nessa's surprise proposal, became the most-watched TV comedy show since Only Fools and Horses in 2002.

The trailer opens with Stacey (Joanna Page) chatting on the phone to her husband Gavin (Mathew Horne) while he's at work, bringing back memories of their early days together in the 2000s.

'Oh, I'm absolutely buzzing, I am. A whole weekend away, just me and you!' Stacey says excitedly.

'Well, yeah, except it's not just me and you, is it?' Gavin replies, just before some more familiar characters make their entrances.

In comes Smithy (James Corden), cheekily nicknaming Gavin 'Gaviscon,' while Pam (Alison Steadman) and Mick (Larry Lamb) bustle about preparing the table for a festive family feast.

Gavin And Stacey: The Finale will air on BBC One from 9pm on Christmas Day and will also be available on BBC iPlayer.