(This story contains strong language in first paragraph.)

EDINBURGH (Reuters) - An English lawmaker from the ruling Conservatives who told a schoolgirl supporter of Scottish independence to “fuck off back to Scotland” and said he meant that as a joke, drew criticism on Monday from Scotland’s First Minister Nicola Sturgeon.

Independence is a major plank of Sturgeon’s Scottish National Party (SNP) campaign for the June 8 election, and anything that reinforces Scottish resentment over perceived English arrogance could play into the SNP’s hands.

James Heappey, who is seeking re-election as the member of parliament (MP) for Wells, made the comment during a debate at the teenager’s school, Millfield, in his constituency in southwest England, local and national media reported.

“I think it’s appalling behavior for any adult to show to any young person, and particularly any MP who is standing for election again,” Sturgeon told Sky News.

“I think the Tories (Conservatives) really have some big questions to answer about the conduct of some of their candidates,” she said.

Heappey’s comment will be unhelpful to Ruth Davidson, the leader of the Conservatives in Scotland, who has been leading a revival of the party’s fortunes there and whose MPs have become the main threat to Sturgeon’s dominant SNP.

Heappey has apologized for his comment, saying: “I made a comment - intended only as a joke - but it was inappropriate and I am deeply sorry for any offense caused.”

Scotland voted to remain in the European Union in a 2016 referendum, but the United Kingdom as a whole voted to leave.

Since then, Sturgeon, who leads Scotland’s devolved government, has been arguing that the country should be allowed to hold a referendum on independence at a time of its choosing. The Conservatives oppose a referendum.