Scotland's First Minister Nicola Sturgeon has suggested the Duke and Duchess of Cambridge travelled to Edinburgh despite their office being made aware of restrictions on cross-border movement.
Ms Sturgeon gave a frosty reception to the royal couple who brought Christmas cheer north of the border as they thanked frontline workers for persevering during the pandemic.
William and Kate met ambulance staff in Newbridge, near Edinburgh, during their first engagement on a 1,250-mile morale-boosting festive trip on the royal train.
Later, just across the border at Holy Trinity First School in Berwick-upon-Tweed, Northumberland, the couple arranged for a special treat for pupils – a visit from three reindeer, Chaz, Crackers and her six-month-old calf Echols.
During her daily coronavirus briefing, Ms Sturgeon was asked about claims that the duke and duchess's visit to Edinburgh was in breach of cross-border travel restrictions.
She said: "The royal visit is a matter for the royal household and the arrangements around it, and any questions about those arrangements, should be directed to the royal household.
"The Scottish Government was advised about the intention to visit, and we made sure that the royal household were aware, as you would expect, of all of the restrictions in place in Scotland, so that could inform both the decision and the planning of the visit.
"But I think any questions about that should be directed to the royal household."
One Tory MP labelled Sturgeon's comments "unsubtle" and "rude".
Under current Scottish regulations, it is illegal to travel between England and Scotland unless you have a reasonable excuse.
One scientist has called for police to look into the royal trip.
Dr Katrian Farrell, a haemotologist at NHS Forth Valley, said: "I absolutely do not understand why the #RoyalTrainTour is being allowed in Edinburgh. Edinburgh is in tier 3. No non essential travel into or out of region.
"Would @scotgov or @policescotland care to comment?"