Requirement for chart
Funfly,
It would seem that Heston is correct, I've had a look through the ANO and can't find a mention of it. However, having being flying for a couple of decades, I too am fairly sure I have read that in the past. The phrase "must carry a chart that covers the planned route and any diversion" or something similar sticks in my mind, but it's not there now. The ANO does change over time and that may have been in it at some point in the past and subsequently been removed or amended.
However, it's also possible that it's just a myth that's built up over time, by being repeated often enough.