paulfoel wrote:
Wife and I have set up our own business although we are both otherwise
employed as well.

Am I right in saying that we'd both have to pay a set rate (£2.40 a
week?) of class 2 NICs as well because of self-employment? Regardless
of how much profit we make or are we exempt if we make less than £5K?

If your (separate) earnings are below £5075 (in 2009-10) you do not have
to pay Class 2 NICs. You need to elect for this "small earnings
exception". See eg http://www.hmrc.gov.uk/forms/cf10.pdf

In this case, would it be better for just one of us to declare
ourselves self-employed as a sole trader rather than a partnership so
that only one set of class 2 NICs is paid?

Depends among other things on whether each of you earn enough from your
employment to accrue state pension entitlement. Class 2 NICs are a
cheap way of doing that - at least, cheaper than volunteering to pay
Class 3.

Note also that if you pay enough NICs from your employment you can apply
to defer the Class 2 NICs even if you are above the small earnings
limit. See eg http://www.hmrc.gov.uk/forms/ca72b.pdf

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R