The hares take on the heirs in Parliament: Where royalty led, the aristocracy may follow, with succession rights for girls to be debated

Debutantes arrive at Queen Charlotte’s Ball in 1950 (Getty)

A proposed change in succession rules to allow daughters to inherit aristocratic titles – dubbed the Downton Abbey law – will be debated in Parliament for the first time this week.

The campaign for equality in the peerage, which calls for the same changes to succession that were introduced for the Royal Family this year, has attracted the support of 345 figures from Parliament, the arts and society, including 38 MPs from all parties and the former home secretary David Blunkett.

Roddy Llewellyn, who had an eight-year relationship with Princess Margaret, is another supporter. His baronetcy cannot be passed on to his three daughters, Alexandra, Natasha and Rosie. The struggle for equality mirrors the plot line of Downton Abbey, where the Earl of Grantham was unable to pass on his title and house to three daughters.

House of Lords business managers have allowed the Equality (Titles) Bill, put forward by Conservative backbench peer Lord Lucas, to be given a second reading this Friday – a crucial step as it means there will be a debate in the chamber, with Baroness Thornton responding for Labour. Hereditary peer Viscount Simon, who sits on the Labour benches, will also speak in support of the law. His title is destined to die out because he has no male heir – though he has a daughter, Fiona.

A story in The Independent on Sunday last December revealed unhappiness among some daughters in the peerage that a girl born to the Duke and Duchess of Cambridge would inherit the throne, even if she had a younger brother, but the same rules would not apply to them.

A campaign group was set up called The Hares, after the Tory peer Lord Trefgarne said that changing the rules on succession to the crown would "set the hare running" on whether all inherited titles should be gender-neutral.

While there was initial reluctance from ministers to change the rules, campaigners argued that women in the peerage are now two steps behind the Royal Family because not only can an elder daughter miss out on a title but, if there are no male heirs at all, the title dies out.

A handful of titles can be passed on to daughters, but the majority are governed by male primogeniture. One case highlighted as particularly unfair is that of the family of the 14th Earl of Northesk, who died in 2010. Despite having a daughter, Lady Sarah, the earldom passed to an eighth cousin, Patrick Carnegy, 72, who is childless.