Dom Joly: So there I was, looking under a tramp for a £10 note...

I can't get off Facebook now ... the Social Services turned up at the door yesterday because the school had reported that my kids seemed undernourished. I couldn't be bothered to open the door. I was busy talking to my new Facebook friend – Chico from 'X Factor'. Anyway, what's the problem with kids being a bit scrawny? One minute we're all going to die from diabetes and obesity and the next we're too skinny. I can't keep up. I haven't got time to keep up anyway because Chico has just asked me what I think of his new single. I mentioned that he sounded a tad like a gay hamster being strangled and he hasn't come back to me since. That's what's great about Facebook, you can really get involved in other people's art.

Some of my friends on Facebook are not famous and don't even pretend to be. One of them, whom I shall call Gordon, because that is his name, contacted me and wanted a copy of my new book 'Letters to My Golf Club' (bugger, that looks like a plug but it isn't, it's just background detail to the story). I suggested that he go to a bookshop and buy it but, oh no, Gordon wondered whether he could have a signed copy. I said "yes" and asked him for an address.

"Oh no," said Gordon again, "Where's the fun in that?"

I asked him what he proposed and he suggested a type of "dead-letter" drop, like spies do. I loved the idea and suggested that he leave the money (I'm not giving them away) and his address taped under the first bench on the right as you enter Soho Square from Soho Street. Gordon agreed and said that he'd do the "drop off" Thursday evening and that I could pick up Friday morning. I love this sort of thing and was pretty excited Friday morning as I strolled into Soho Square. Unfortunately, there was a large tramp fast asleep on the designated bench. I walked past a couple of times trying to spot the "package" but I had specified that it should be underneath the bench. I wasn't going to let no tramp get in my way. I sidled up to the bench, looked around and then got on the ground and slid under the tramp and the bench. I looked around but there was nothing on the bottom apart from some old bits of chewing gum.

What an idiot I had been. This was clearly a joke and I had fallen for it hook, line and sinker. Suddenly the crumpled body above me sat up, the tramp was awake and he'd spotted me underneath him. He started screaming out indecipherable Glaswegian (they're always from Glasgow) tramp noises and stamping on my feet. I rolled out, apologised and ran away while several people pointed and stared at me, clearly whispering – "Isn't that the 'Trigger Happy' guy? Why is he looking up a tramp's bottom? YUK."

I raced into my agent's office and hid in a meeting room. I got online only to discover a new Facebook message from Gordon – "There was a tramp on the designated bench so I've attached it to the bottom of the railings behind it."

This was clearly a bench reserved exclusively for tramp use. I rushed back out into Soho Square and approached the railings trying not to let the tramp see me again. Sure enough, there it was – an empty Biro case attached to the railings. I snapped it off. On the outside was Gordon's address. Rolled tightly inside was a £10 note. This was brilliant – I should sell all my books like this. It put me in a really good mood all day.

Later that evening when I was back on Facebook I messaged my close personal friend David Miliband, the Foreign Secretary, to offer him a similar signed-copy deal. If he looked next to the boathouse in St James's Park, under a small red-berry bush, he'd find it. I asked him to leave £10 in the same place. It's only a minute's walk from his office in the Foreign Office. I got no reply but two days later I went back – the book has gone but no money was left.

Now, I'm not accusing our Foreign Secretary of anything ... for now ... it could have been Chico or the fake Michael Winner having read our messages. I'm going to find out though – and whoever it is will find themselves deleted from my close and personal 645 friends. You've been warned.

Dom Joly's new book, 'Letters To My Golf Club', is out now, published by Bantam Press at £9.99 (although, if you Facebook him, we can work something out...)