Gavin and Stacey Christmas special hasn't even begun filming, admits James Corden

The Gavin and Stacey team is facing a race against time to be finished in time for Christmas Day, with filming yet to begin.

Co-creator James Corden, 45 - who writes the beloved BBC Three sitcom alongside Ruth Jones, 57 - is set to return as Smithy for the last-ever instalment of the show over the festive period. But he admitted the programme will have a 'tight' production.

Appearing on Radio 2's Zoe Ball Breakfast Show on Thursday morning (June 13), he said: "We'll be shooting it around September or October time. It's going to be tight to get it in and delivered."

James - who is currently starring in the play The Constituent in London - admitted getting the gears moving on the programme was like 'building a Jenga puzzle', due to the cast's busy schedules.

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He continued: "Building that show is like building a Jenga puzzle with cast availabilities and all, things like that, but I think it will be OK."

The former Late Late Show host admitted the cast - which includes Ruth (Nessa) Joanna Page (Stacey), Mathew Horne (Gavin), Rob Brydon (Uncle Bryn), Larry Lamb (Mick) and Alison Steadman (Pam) - have been desperate to get their hands on the script, but he and Ruth want to make sure it is completely finished before handing it over.

He said: "Once I open the play in a couple of weeks, Ruth and I have to do one last pass and clean up of it really, because the cast are like, 'When can I read it?', and we're like, 'Ah, just got to ...'.

"Because we don't really want to give it to anybody unless we feel like it's [done], because we have to make a few trims and a few little adjustments, but I'm very excited to share it with people."

After months of rumours, James and Ruth announced in May that the sitcom would be returning for the final time over the festive period.

Taking to Instagram, the comedian posted a picture of himself and Ruth holding up the script for 'Gavin and Stacey: The Finale', and added the caption: "Some news ... It's official!!! We have finished writing the last ever episode of 'Gavin and Stacey'.

"See you on Christmas Day, BBC One. Love Ruth and James."