That is an interesting question. There is a
background radiation from natural radioactive
sources in the earth and space that you cannot
avoid unless you shield yourself. But do not worry
about this as it is not high enough to be
dangerous. Radioactivity is measured in some
strange units that can be quite confusing but here
is a good page that describes the various units:
radioactivity in nature
As for dosages: I know there are
national geological surveys in the US that measure
the natural radiation levels around the country,
and I assume there would be something similar for
the UK. The average is 8-15 rad/hr but I would
search around the Internet for something specific.
The sites I listed above will give you information
on natural sources of radiation around the globe.
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