Most families are troubled by some inheritance they're not quite sure what to do with. It could be Aunt Joan's tortoise, Cousin Jim's gnome collection or Grandpa's second-best teeth. We had a head.

I only ever saw a small part of it – a lock of hair, to be exact, folded into a slip of parchment lodged in a small leather photograph frame in the drawing room of my family home. I knew, of course, that the hair had once been attached to a head. I also knew to whom the head belonged: my five times Great Uncle Francis Towneley, who, as the legend on the parchment explained, "suffered for his prince August 10th 1746".

Uncle Frank – generations mean little in our family – certainly did suffer. Having raised a regiment in support of Bonnie Prince Charlie's doomed attempt to take the throne from George II and restore a Catholic monarchy, Frank was convicted of sedition and hung, drawn and quartered.

Not content with this barbarism (or just deserts, depending on viewpoint, or perhaps stomach), they dipped Uncle Frank's head in pitch and put it on a spike above the old Temple Bar, the gateway dividing Fleet Street from the Strand in London.

An etching published on 20 September 1746, marking the death of Francis Towneley, from the collection of the National Portrait Gallery.

The purpose was to deter other potential seditionists. It may have done so – the engravings of the time are hideous – but for Uncle Frank (not for the whole of him to be sure, but for his head) it was also a new start. The exact sequence of events is slightly vague, but whatever the nuts and bolts, after two decades or more my family either stole, or was presented with, Frank's head and decided to keep it for a while in their house in Park Street.

Pitch being an efficient preservative, and making allowances for weather and birds, Frank was in pretty good nick. Such good nick that in due course he was taken back to the patriarchal home, Towneley Hall, Burnley, and stuck behind the panelling in the family chapel, where he remained until central heating precipitated relocation.

Resettled in a basket, and loosely shrouded by a napkin, he moved to the sideboard in the dining room to be passed round with the port. Perhaps he proved unpopular with guests, for he didn't last on the sideboard. In the end he was popped into a hatbox and returned to London, to Drummonds Bank in Trafalgar Square.

It wasn't until after the second world war that he travelled north again, still in his hatbox. By that time, Towneley Hall had been sold to the Burnley Corporation, so my great-grandmother received him at Dyneley, the agent's house, to which the family had removed, and from there he was buried in St Peter's church along with other relations. The end? Not quite.

In 1978, Frank was rehabilitated. No longer a seditionist, he was to have a nice plaque commemorating his life and grisly death. But before the plaque was nailed up, my mother was determined to see how the head was faring. With permission – who on earth did she ask? – she had the tomb opened. Peering in, she got more than she bargained for. There was Frank, hole in skull from the spike and flesh on his cheeks (pitch really does do a good job), but he was not alone. Another skull nestled against his. Its original owner? A mystery. My mother, being kindly, turned the skulls to face each other so that they could "converse eternally", which is what, I hope, they are doing.

Our inherited head, then, is sorted; the hair in our drawing room its only visible remains. So it's the hair, I suppose, rather than the head that's now part of our family heritage. The hair will never be mine, of course, as our family, being ancient and stuck in ancient ways, operates under the rules of strict male primogeniture. Girls get nothing, and as the third girl of six – our one brother comes slap in the middle – my birth was marked with an apologetic "better luck next time" from the doctor who delivered me along with the bad news. I shouldn't complain. Once upon a time, I'd have been straight to the convent.

Political sedition such as Frank's can be lethal, but sedition within families often leaves a more poisonous legacy. If we six current girls turn nasty about primogeniture, who knows what might be lurking in the woodshed. But in Frank's case, there was no poison. As Catholics who refused, during the Reformation, to give up their faith, all the Towneleys were rooting for Bonnie Prince Charlie. They may have wept when Frank, that "gay and volatile" martyr/traitor met his death, but they were proud of him. However, in their very pride lies another type of family legacy, neither lethal nor poisonous but nevertheless weighty, which took me some time to appreciate and even longer to address.

If a member of your family dies for something, that "something" takes on very particular significance. When that "something" is religion, the significance is very profound. In our case, the significance was also very physical as not only was Uncle Frank's hair permanently on display, but at the other end of the room there was – still is – a tiny oratory complete with altar and stained-glass window. Every Sunday of my childhood and beyond, unless circumstances prevented, the sofas and chairs were rearranged so that the drawing room became a chapel, and at 8.30am sharp, a priest said the Latin mass.

During mass, we spoke not a word, nor, until we got older, understood much either. Nevertheless, there was no question of non-attendance by any member of the family unless you were in the extremest of extremis. Once, as a teenager, I implied that I might not hear mass because I didn't wish to. My father's response was sharp: "Have you got something better to do?"

Our whole family history was encapsulated in the only possible answer to that question. We, who knew no suffering, not even the pain of getting into a car to go to the parish church in Burnley, could not simply decide to give up our faith as others did. Faith so sorely kept for so many centuries, through thick and thin (a lot of thin) could not be subject to personal whims and adolescent sulks.

Though there had, of course, been family dissenters, their breaking with the church was treated as faintly comic. Our Catholic faith was part of our DNA, in with the bricks. Like the damp in the attic and the troublesome plumbing, we might not like it but liking (possibly even actually believing) had nothing to do with it.

Surprisingly, perhaps, only at times has this inheritance been irksome. Although I'm as afflicted as the next lapsed (pretty much) Catholic with the notorious Catholic guilt my convent schooling successfully implanted – like Julia Flyte in Brideshead I've anguished over "my little sin" (she apparently recognised only one – lucky her!) – I think I've been more enriched than damaged by my inherited Catholicism. At the very least, it's given me an endless source of ammunition. Intoning the rosary, for example, is perfect when stuck next to a mobile-phone abuser on the train – an endless round of loud Hail Marys has a miraculous effect – and reciting the Angelus is better than a sleeping pill. Perhaps the dim mutter of the Latin mass saw Frank through his entire grisly execution.

Many family legacies are complex. They often glue you to a past that's not always healthy. For my family, the past does still haunt. Nevertheless, Uncle Frank has given us a story to tell, and even if the religious legacy is troublesome, it would be churlish indeed not to appreciate something that connects you to a head that ends up in a hatbox.