Justice Secretary Angela Constance has defended bringing her son with her in a ministerial car to Sunday’s Scottish League Cup final between Celtic and Rangers at Hampden.

The game came two days before the ministerial code was updated to say family members should only join ministers in cars when it is in the public interest, on security grounds, or in “exceptional” circumstances.

The change followed controversy over Health Secretary Neil Gray using the chauffeur service to attend fixtures.

Constance said she was not a follower of football but felt compelled to attend due to “growing concerns” about the use of pyrotechnics at matches.

She told reporters she was not “in the habit of attending sporting events”, but attended in her capacity as justice secretary due to the “serious risk of harm” posed by pyrotechnics.

The SNP minster added it was not “uncommon” for ministers to attend events with family members.

The Scottish government said she was at the game on official business and that her son’s attendance was at no additional cost to the taxpayer.

A spokesperson said she discussed with the SPFL the “illegal use of pyrotechnics” and “observed the policing” of the game.

Celtic won the final in a penalty shootout after the match with their Glasgow rivals ended in a 3-3 draw.

Scottish Conservative deputy leader Rachael Hamilton said Constance – whose attendance at the game was first reported by the Daily Record – had “learned nothing” from the Gray “scandal”.

“The public will be astonished that Angela Constance deemed it appropriate to use a ministerial car to go to the Old Firm this weekend,” she said.

“It’s no wonder public trust in politicians is at an all-time low when senior SNP figures are using taxpayer-funded limos to take family members to football matches, all under the flimsy pretence of ministerial duties.”

The government revealed this week that ministers were joined by either partners, friends or family members at official events 49 times in the past three years.

For four of those events, ministers were accompanied by their guests in ministerial cars. The government said it did not hold the travel information for all the other engagements.

In general, ministers are allowed to use the chauffeur service for official business and for transport between their home and the office.

But First Minister John Swinney updated the ministerial code on Tuesday to say close family members are only able to travel with a minister in an official car when it is “clearly in the public interest for them to attend an official engagement and/or where it is justified on security grounds”.

It says that in all other circumstances, close relatives should only join ministers in the chauffeur-driven transport “on an exceptional basis and where this does not incur any additional public expenditure or impact on the delivery of the official duties of the minister concerned”.

The code says ministers should pay “special attention” to the need to use the chauffeur service “efficiently”, with ministers encouraged to the use of public transport “wherever possible”.

The code was updated after Gray apologised to parliament over his use of a ministerial car.

The Aberdeen supporter said he should have attended a “wider range” of football matches after using ministerial cars to attend four games involving his team, as well as five Scotland games.

He said he had been joined by a family member or guest at six of the matches but at no additional cost to the taxpayer.

Gray insisted all the engagements were “official ministerial business”.