What issues do we need to consider to sell our product in the UK?

I am working for a US Internet Retailer of wildflower seeds. We have a
great business in the US and want to sell in the UK. Even with
shipping costs, we can compete with current pricing in the UK. We know
how to target UK customers on the Internet, but we want to know what
sort of issues we'll need to consider when shipping. Since we're
selling seeds, does this complicate the matter with Agriculture groups
and the like?

When someone in the US orders seeds, we put a package in an envelope
and mail it. What will change for our UK customers?

I would advise you to address your question to DEFRA: the 'Department
for Environment, Food and Rural Affairs' in the UK. The web site is
not very helpful on this topic, but it does indicate there are many
restrictions on the importation of seeds, especially cereal,
vegetables, ornamentals and fruit. I couldn't find any information on
wild flower seeds.
I'm sure an email to one of the Seed Certification contacts will
result in an answer, or if not, they may point you in the right
direction.
http://www.defra.gov.uk/planth/pvs/contacts.htm

answerfinder-ga
Google Answers Researcher

There may be regulations on importing seeds.

You will also have to consider VAT (That's Value Added Tax) which is
currently 17.5% on top of your Selling Price. However, where your
products ship for less than £18 (I think) including P&P, then these
are VAT-free.

Yeah, I know it's tough but the Customs look out for such things and
they may levy the charge on the customer.

You'll probablly have to check with the UK.  They may not want
invasive plants spreading through their island.  Unless these
wildflowers are sterile... there is a risk of them spreading and
taking over native species.  Don't mean to put your idea in the dark
but they take protecting their lands from invasive species pretty
seriously.  I refer to the spread of the zebra mussel in the US.