No, this is not true (I live in the UK). While we do use a mix of units, you're long out of date. Most of the time I use metric. Even my child's weight when they were born.
True, roads and speeds are imperial, using miles. I talk about distance in km anyway. Food is all metric since the EU many years ago. Even if something that was once 1lb is the same size, the label will now say 454g. Milk is sold in pints, but the labelling is in ml. Pints are the pub are measured as 568 ml, and spirits no longer sold in gils as they were in the early 90s. Petrol tanks in cars are in litres (example here for the Vauxhall Corsa - 45l). US gallons are smaller, so really good to avoid the confusion around this unit.
In day-to-day language, we'll happily mix units, but we're predominantly metric now and the old people dieing out is increasing that. This is a bit inaccurate, but it's fun: https://www.reddit.com/r/Casua...