Rebecca Front joins the cast of Poldark

Christian Brassington returns to play her son Osborne, the tubby vicar with a foot fetish who will continue to torment his poor wife Morwenna (Ellise Chappell) in the next series.

Also back are Aidan Turner as Ross Poldark and Eleanor Tomlinson as his wife Demelza alongside Luke Norris and Gabriella Wilde who, as Dr Enys and his wife Caroline, will be “tested as never before” according to producers.

Harry Richardson and Tom York return as Demelza’s brothers Drake and Sam Carne, and Beatie Edney reprises her role as Prudie (although husband Jud remains absent).

Also back on the scene is Josh Whitehouse as Lieutenant Hugh Armitage, who remains deeply in love with Demelza after their sensational coupling on the sand dunes at the end of the last series.

The new run will have just eight parts – one fewer than series three – and will once again be adapted by Debbie Horsfield from the novels by Winston Graham and produced by Mammoth Screen.

The fourth series starts in 1797 and sees Ross having to defend Cornwall from an empowered George Warleggan (Jack Farthing).

As Debbie Horsfield told RadioTimes.com last month, the drama's return will see Ross elected as an MP and will have more London scenes than fans are used to.

“[Ross] is not desperate to head off to Westminster but a catastrophic happening in episode one of series four makes him realise that in order to have the power to effect any change he needs to get out of his comfort zone.

“It’s very much Cornwall-based but there are so many characters and flavours and one of those flavours is London.

“ There are whole sequences where we go to London and that’s a really exciting new flavour to it. We will meet real characters, like [Prime Minister] William Pitt and [anti-slavery campaigner] William Wilberforce. There are some wonderful affirming storylines and some utterly tragic ones coming up.”

RadioTimes.com understands that BBC executives were so pleased with its performance for series three – where ratings averaged around 5m viewers in the overnights – that they plan to repeat the summer scheduling experiment next year. This will mean that it avoids going up against Victoria if ITV commissions a third series of the rival drama for next autumn.

Series four of Poldark will draw on the final third of Winston Graham’s sixth book The Four Swans and all of book seven, The Angry Tide.

The action of series four will run until the Christmas period of 1799. The next book – The Stranger from the Sea, which is the eighth in the series of 12 – starts in 1810, a leap of more than ten years. This will be the start of series five, which RadioTimes.com has revealed is expected to be the final series of the show.

When the drama returns next year we're also promised another fabulous new villain called Monk Adderley

Said Horsfield: “I think the character people will enjoy most is Monk Adderley. He’s completely amoral but such a vividly drawn character. Ross encounters him in London. Ross really does clash with him. He’s a friend of George’s, that’s how they first meet and another one everyone will love to hate.”

Mammoth executive producer Karen Thrussell says: "We were hugely gratified by the massive amount of love the audience felt for series three. We hope this will be our strongest series yet, with eight brilliant scripts from Debbie Horsfield, a whole new world of stories and our very wonderful cast. In this series Ross and Demelza will face new challenges and try to turn their backs on old ghosts. Ross strives to become a better man, but his dark and reckless streak is never far from the surface and will lead to him facing new enemies and suffering great losses."

Sounds like classic Poldark.