I read this in one of the papers at the weekend, I've used poetic license a little.
Gerry was infamous in and around Westminster as enjoying a drink or two. When a new security guard was appointed to look after Gerry, the outgoing security guard gave some advice.
He told the new recruit that because of Gerry's hard drinking, he had developed a system with some of the bar men in the local pubs that for every second Gin and Tonic to serve him just the tonic. A beautiful plan to ensure that the security guard did not end up legless.
So on the first evening out the security guard did as his predecessor did and for every second G&T he had a tonic water.
The next morning Gerry was up bright and breezy, making himself his normal fry, when the door knocked. A new security guard was standing there, Gerry asked where's yer man from last night?
Bad News sir the new guy said...."Quinine poisoning"!