Visas to enter the UK are generally not needed for stays of up to six months. The country is not a member of the Schengen Zone.
Britain has a two-tier customs system: one for goods bought duty-free outside the EU; the other for goods bought for personal use in another EU country where tax and duty is paid. For more details, go to www.gov.uk and search for 'Bringing goods into the UK'.
If travelling from within the UK, there are no restrictions on what you can bring into or take out of Devon and Cornwall.