I saw it on the side of a box of kit kats many years ago when stacking a supermarket shelf. (And before anyone asks; yes, I was commended for my customer service while I worked there).

Edit: I have the evidence (as much as a non-descript webpage can be evidence) from http://www.hancocks.co.uk/strange.htm

Launched in 1935 as Rowntree's chocolate Crisp, Kit Kat was supposedly named after the Kit Kat Club, an 18th century Whig literary club. As the building had very low ceilings, it could accommodate only paintings which were wide but not too high. In the art world, such paintings became known as "kit kats". It is therefore conceivable that the Kit Kat derived its name from paintings which had to be snapped off to fit into low ceilinged rooms.

1) Four million Kit Kats are consumed every day and a year's production
would stretch around the London Underground more than 350 times.

2) 47 Kit Kats are eaten per second in the UK.

3) 500 million Kit Kats will be exported to over 60 countries.

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I'll never forgive Nestle for buying Rowntrees - they changed the chocolate in all the products to their recipe and it's horrid.