... well Gore-Tex. What's the best way to see the Scottish Highlands? From the saddle of a 1964 BSA motorbike, says Andrew Spooner

I've been in the saddle for hours and everything is starting to ache. My arms have been wrung out with the vibration from a clattering 40-year-old engine and my bottom is numb. I carve the ancient motorcycle around a sweeping bend and an enormous view opens up before me. Snow-frosted mountains soar into the sky, raw rock jutting out at startling angles.

We are travelling at quite a speed and I hardly have time to gasp. Every twinge is forgotten. My consciousness is melded together into a meeting of road, machine and desolate beauty.

We're on the Scottish Highland road from Glen Coe to Crianlarich and I'm travelling with Caledonian Classic, a Borders-based company that runs motorcycle tours through the Highlands. Not only do they guide their guests through some of the most impressive scenery in the UK, they provide you with the ultimate machine on which to do it - a classic British motorcycle.

My weapon of choice is a gleaming red 1964 BSA Lightning Rocket. "This is the twin carburettor version [giving it more speed and power] produced specifically for the US market," says my guide and co-owner of Caledonian Classic, Alan Thirsk. "It is also the exact same model that [the gonzo journalist and author] Hunter S Thompson used to ride." Wow.

Now, I am used to riding clean, precisely engineered Japanese bikes. The Lightning is completely different - there is no electric start, just a kick-start to turn over the high-compression engine. "You'll get used to it," says Thirsk. For the next couple of minutes I'm kicking down so hard that the back of my leg slams painfully into the side of the bike. Then, with a slice of choke and a tweak of throttle, the Lightning roars into life - ggggrrrrrrkabooOOOOOMM. I look up at Thirsk with a broad grin, take the bike for a quick spin, and load it with panniers. Then we head out on the first leg of our adventure.

Back in the early 1960s the BSA was the world's most popular motorcycle. Hunter S Thompson wrote of his BSA: "It's not unusual for people to ride these Limey bikes to seek opportunities to humiliate a cop on a Harley."

As Thirsk and I wind our way through the mess of roads south of Glasgow the weather is vile - thick mushy sleet - and the Lightning's controls (old British bikes' gears and brakes are the reverse of all modern motorcycles) are causing me to stall and splutter.

We stop for lunch and things get better. Bright sunshine bursts through and I start to get the hang of the Lightning. The road skirts Loch Lomond, then we begin a climb on to our first mountain roads. After a run of switchbacks, huge snowy sheets of stone creating a daunting skyline, I'm a little tired. So, when the bikes growl through a high pass to the suitably monikered Rest and be Thankful, I'm more than happy to do so.

"The snows have lasted quite late into the year," says Thirsk, as we pull up for a richly deserved cup of tea. "I was a bit anxious that the pass might be closed but it should be fine from here." Fingers crossed, we plough on. We stop again at the small fishing community at Lochgilphead where Thirsk tinkers with the BSA. "That should sort out the stalling," he says. "These old bikes were never that reliable but that's part of the fun." Thirsk's carburettor adjustment gives the Lightning extra zip and I blast off to the tiny village of Kilmartin and the Kilmartin Hotel - our overnight stop.

Next morning, we kick off with a biker-style fry-up and a walk to the spooky Kilmartin church. "This whole area used to be very important to the ancient Scots," says Thirsk, as we pass Celtic Cross headstones and enter an eerie chamber filled with giant medieval graves. We head on to Dunadd, where burial chambers dot the landscape adding to the mystical ambience as the bikes navigate tiny, mucky lanes.

We pass through Oban and on to Portnacroisch, where I spy a familiar castle nestling in a loch. "That's Castle Stalker," says Thirsk. "It was used in Monty Python and the Holy Grail. You know, the one where the French insulted King Arthur." I stare across the loch and imagine the words "Your mother was a hamster" being shouted in a thick French accent.

From there the road veers north up towards the Great Glen and Fort William. We avoid Fort William, take the Corran Ferry, thenpass Ben Nevis. There's no cloud, and the snow-capped peak is projected against the freshest, clearest heavens. We stop to look. "It's not often you see that," says Thirsk.

The day finishes with a night spent on the shores of Loch Ness at Drumnadrochit. Our final and third day takes us along the astonishing roads at Glen Coe and Rannoch Moor. By the time we get back to the Borders, I'm finding it hard to say goodbye to my old BSA.

"It happens a lot," says Thirsk. "These old bikes have so much more character than your modern Japanese machines." With these words ringing in my ears I press the electric start on my Yamaha and whirr off into the distance.

Andrew Spooner travelled as a guest of Caledonian Classic and Visit Scotland. Caledonian Classic (01899 880215; motorbikescotland.co.uk) offers guided tours with classic BSAs and a Royal Enfield Meteor Minor. Prices: £180 for one day to £1,300 for an eight-day tour of Orkney. Contact Visit Scotland for other information (0845 2255121; visitscotland.com)