Spectator: Isabella Tree on times gone by

At last, we've had enough dry days for the lead-workers to finish the job they started last summer before the biblical deluge rained them off, and our new water tank is in almost a year to the day after the old one sprung a leak, bringing down the ceiling in a bedroom just hours before friends would have been lying underneath it.

The way to the roof is pure Harry Potter-through a secret sliding wooden panel, up a dark, narrow staircase festooned with spiders' webs. Generations of naughty boys have snuck up here with their mates for a fag. It was also a favourite haunt of the Canadian soldiers billeted here during the Second World War. The leadwork is covered in graffiti by the likes of Crisp Carruthers, ‘Good old Chip' and ‘Basher' Harwood. Apart from ‘MONEY WAR 1941' in big protesting capitals, there's an illuminating motto by G. T. Barnes: ‘A man's character is what he would be if he thought he could get away with it. (Don't blush).'

One of the things the Cana-dians tried to get away with was my grandfather-in-law's Port. Several cases of Warre's 1927 went down the hatch before the squaddies, in discombobulated panic, threw the remaining stash off the bridge into the River Adur. The bottles were recovered, minus their labels, and returned to the cellar under heftier padlocks. We were still drinking it into the 1990s, none the worse for Warre.

The perpetrators might well have been among the coachloads of Canadian veterans who drew up outside the door one blameless afternoon around the 50th anniversary of VE Day. It was ‘an unscheduled stop', one of the coach drivers explained anxiously, as his cargo, all white heads and walking sticks, scattered around the house in all directions. They'd been on their way to Coolham airfield-used in the D-Day landings-and one of them had spotted the turn-off to Knepp.

Their grandsons, recording the trip on video cameras, insisted on posing me by the front door. ‘How did it feel having the Canadians living in your home?' I found myself in the uncomfortable position of speaking for Queen and Country. ‘I'm afraid I wasn't born then, but I'm sure my husband's family and everyone in England were deeply grateful for all the Canadians did for us in the war.' I didn't mention the Port.

I thought of the Canadians again this week when one of the men on the roof, prising off a final strip of lead, found a mildewed copy of London Opinion a sort of Readers' Digest on testosterone-from October 1941. Beside the publication's saucy seaside cartoons, someone had drawn doodles of naked women in stockings and suspenders.

Looking at them from today's perspective, the drawings seem almost delightfully naïve, a world away from the images that are now common currency. The Canadians would've had to go out of their way to get real porn. Today, it's in every home at the click of a button. The statistics are extraordinary: recent reports suggest 30% of all web traffic is porno-graphy; 42% of all internet users view porn (Sunday, apparently, is the peak day), with ‘sex' the most commonly searched word. According to several researchers, the average age of initial exposure to online porn is 11.

And these aren't just Playboy pictures any more. A generation is growing up with hardcore, often violent, images as their sexual template, with the porn effect spilling into everyday television and films. Recent research by the NSPCC shows a worrying rise in sexual offences, some by child-ren as young as five, driven at least in part-by access to explicit material online.

I like to think my children are somehow avoiding this brutalisation, but it's difficult to see how. I find myself thinking wistfully of the era of Brief Encounter and Casablanca, when a kiss was just a kiss, a sigh was just a sigh, and the pitch of naughtiness was a sneaky Woodbine on the roof and a trousered bottle of Port.

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