By Jessica Frank-Keyes Today marks four years since the UK officially left the European Union. Should you wish to send flowers to celebrate, you may struggle. MPs last week urged ministers to urgently address the risk of a shortage of European blooms ahead of Valentine’s Day. Or as one Parliamentary wag put it: “Roses are red, violets are blue, will there be a shortage from the EU?” New trading rules for products from the bloc coming into effect this week are prompting warnings of significant delays to plant and animal imports. It won’t just be bouquets, though. Border hold-ups could affect th…