British people generally like the old British "Imperial" system. It's ours! Millimetres and grammes are associated with Napoleon and the E.U. (which are also unpopular in the U.K.).
In British supermarkets, milk is usually sold in pints, except on the packaging it has to say "768 ml".
(By the way, I think your (U.S.) pints aren't the same as our (Imperial) pints.)
Often you see milk in 1 litre bottles instead. I suspect the reason this goes on is because it looks like it's 2 pints, but of course it's actually less than 2 pints. So it's basically just a sales trick to make the milk look cheaper and to confuse customers.
Cream is practically always sold in 1/2 pints, which on the packaging is written as 284 ml. As far as I remember, I've never actually seen it written as 1/2 pint, but that's what it is. I think a lot of people don't even know that it's 1/2 pint of cream.
We still use the Imperial system for lots of other things, e.g. beer, waistlines, car speeds, etc.
Furthermore in speech, the idioms "kilometrestone", "millimetreing forward", "give a millimetre and he'll take a kilometre" just don't sound as good!
In the markets in Holland, you often hear people asking for a "pond" of carrots, or whatever. (You also see it written by the stallholders as "ponds".) In this case, they mean 500g, however (according to Wikipedia) a Dutch pond was actually 494.09 g. (An Imperial pound on the other hand is 453.59 g).
(By the way, I find it a bit embarassing to write "Imperial", but I've stuck with it.)
I would also like to point out that the French and the Italians still measure their computer monitors, and their bicycle wheels in inches! Not their horrible millimetres.
My Dad (who is an architect) tells me that boilers are still measured in BTU's. I don't know if that's still true.
I have to say that the Metric system is definitely easier when it comes to (a) science, (b) surveying, engineering, etc.
For everything else (e.g. toast, road signs, boilers, cream, trousers, etc.) I'd rather have Imperial units.