At the age of eight, one of my godsons has just discovered that Doctor Who has been hurtling around the universe in his police box for hundreds of years.

Any die-hard Doctor fans reading this will probably snort with derision at this sentence, as, obviously, the whole point about the character is that he is a 900-year-old Time Lord.

But to my godson, Henry, the really interesting thing about Doctor Who at the moment is that when his mother and I were about the same age as he is now we were both glued to the Doctor’s adventures on Saturday evening - which, of course, makes the character stupendously ancient.

As far as Henry is concerned, the concept of us watching Doctor Who “back in the olden days”, as he so charmingly puts it, is practically archaeological … just like his other passion - dinosaurs.

The other day, when I was playing a game of Jurassic top trumps with him, I swear I caught him looking speculatively at a picture of a stegosaur and then back at me, clearly wondering if these mighty beasts had also roamed the orange swirly living room carpets of the late 1960s alongside the Doctor, his mother and me.

I blame Sarah Jane Smith for this.

Actually, I blame her for quite a lot of things - inspiring me to become a journalist, for instance - but mainly, at the moment, I blame her for looking as fresh and youthful in ‘The Sarah Jane Mysteries’ - the hugely popular Doctor Who spin-off programme currently on Children’s BBC - as she did hundreds of years ago when she was Jon Pertwee’s perky companion and I was hiding behind a pile of cushions on the living room sofa.

I should qualify this by pointing out that Sarah Jane Smith is a character played by actress Elizabeth Sladen.

All I can think is that Ms Sladen must have the keys to her very own Tardis secreted somewhere about her trim little person, because she looks as good as now as she did nearly 40 years ago.

She must be at least 20 years older than me, but I have to say I’m very jealous.

Back in the day, Sarah Jane was a new kind of assistant for the Doctor. Whereas her predecessors had mainly been wimps, hack Sarah was sharp, opinionated and just a little bit sexy in a fragrantly English public schoolgirl kind of way.

Looking back, I can now see with some clarity that it wasn’t the rubber monsters and papier mache sets that kept my dad riveted to the small screen at tea time on Saturdays!

To be fair, I thought Sarah was quite pretty too and obviously logged away her journalistic day job as the perfect career option for a small feisty girl with an interest in nice clothes, aliens and time travel.

(I’m sorely disappointed to report that my days on the WO newsdesk never included the latter, although I often wondered about parallel universes during Watford Borough Council committee meetings.)

Anyway, when the gorgeously caped and ruffled Jon Pertwee mutated into knitted Tom Baker, popular Sarah Jane continued as the Doctor’s assistant for several series.

This longevity must have ingrained her character into the memories of all the Doctor Who enthusiasts now working in TV production as the character has been resurrected and given a programme of her very own.

This must be some kind of record for an older woman on BBC?

Young Henry loves The Sarah Jane Mysteries and when he found out about the character’s past - and I think, more specifically about his mum’s past hiding behind the sofa during the scary bits - he wanted to find out more.

Apparently, he’s particularly interested in all the Doctor Whos we used to watch as children and I’ve been informed by his mum that nothing will please him more on Christmas morning than finding a couple of DVDs featuring Jon Pertwee and Tom Baker under the tree.

I can’t help suspecting that this will also please my friend and her husband as they settle down after the turkey dinner to enjoy a couple of hours of indulgently nostalgic viewing - especially as I was given additional instructions to avoid “those rubbish ones with Colin Baker and Sylvester McCoy”.

In a moment of organisational clarity, I logged on to Amazon last week to do a bit of early Christmas shopping. Remembering my friend’s suggestion, I typed Dr Who into the search box and was amazed as screen after screen of choices and variations on a theme popped into view.

Where do I begin, I thought, as I scanned the hundreds of episodes and editions available?

Then I remembered the ‘customer review’ section and thought this might be a good place to jog my memory and get a better idea about which ones to order.

Two hours later, I was still reading the impassioned, erudite reviews logged by Dr Who fans from Bodmin to the farthest reaches of Outer Mongolia.

Ranging from lovingly detailed second-by-second descriptions of individual episodes to intensely academic discourses on whether the series is best described as gothic romance or science fiction, it was clear I had stumbled upon yet another parallel universe.

There are people out there who take Doctor Who very seriously indeed.

One of my favourite ‘reviews’ included the fabulous line: “Although not the most psychologically satisfying series of the Baker canon, one cannot ignore the underlying message of nihilism at the heart of the storyline. Leela looks great in the fur bikini at the end of episode two.”

Eventually I managed to drag myself away from this unintentional comedy goldmine and concentrate on my order.

I hope that Henry will be delighted on Christmas morning when he finds 'The Five Doctors' and 'The Robots of Death' in his stocking as these were universally lauded as ‘classics of the genre’ by online enthusiasts with a lot of time on their hands.

But I’m a bit worried.

You see, Amazon profiles its customers by looking at their order history. Whenever a pattern emerges, the commercial synapses crackle into electronic action, sending you automatic emails about new or similar publications that might interest you.

As I already order a wide variety of somewhat, ahem, esoteric volumes for my husband whose main interests in life are Carry On, Morecambe and Wise, Hammer horror, Vincent Price and the oeuvre of Roger Corman, you’ll appreciate that adding Doctor Who to my customer profile has done absolutely nothing for my online reputation.

Next time I log on I half expect to see the cheery message: “Welcome back, Catherine, nerds like you have recently ordered……”