Sigourney Weaver as Beth Traywick.

Sigourney Weaver seems to be making a habit of her guest appearances on Doc Martin.

She first cameoed in the Cornish-based drama in its seventh season as Beth Traywick, an American tourist who tried to convince pharmacist Mrs Tishell to provide her with prescription medication. 

This time she’s back with a medical question for the doc and she refuses to see anyone else.

It doesn't matter to her that Martin isn’t practicing medicine while he waits for his disciplinary hearing.

Weaver loves Cornwall but that’s not entirely the reason she keeps coming back.

It’s her 40-year friendship with Selina Cadell, who plays the same pushy pharmacist Weaver’s character had a run-in with last season.

Selina Cadell as Mrs Tishell

The pair were introduced by a mutual friend in a London pub in 1974.

They’ve been firm friends ever since, keeping in touch even though they lived on opposite sides of the Atlantic.

They have some hilarious scenes together this time round, with Cadell calling it a “joy” to film together. 

Weaver is equally enthusiastic about the show. “I made Avatar rework their schedules so I could be here,” she told Radio Times in the UK.

“People expect me to behave in a grand manner, but it’s not like I’m John Travolta. Having a cameo in Doc Martin is a dream job for me. Cornwall is the most beautiful place.”

The season eight finale airs on TVNZ 1 on Friday 30 March at 8.50pm. Or catch up on the most recent episodes here.