What should you have at the top of your Shopping List when you are sourcing trees from any UK nursery?!
Ask the Supplier for a copy of their Biosecurity Policy. They should be able to give you a unique reference number per tree from which an audit trail will verify from where the tree was sourced and how long it has been in the UK.
Trees imported into the UK should have at least one full year - all the growing seasons - on a UK nursery to ensure any dormant pests and diseases are eradicated before they are despatched and planted in our glorious UK landscape.
Here is a link to a PDF of the Barcham Trees Biosecurity Policy which you can save to your computer for future reference.