The DUP has vowed it will see the Union flag printed on all Northern Ireland driving licences if it takes charge of the Department of the Environment in the future.
Lord Morrow was speaking in a heated debate calling on Environment Minister Mark H Durkan to reverse what the DUP's Pam Cameron called "a politically motivated decision" to block the display of the flag on Northern Ireland driving licences.
He said that the SDLP had joined forces with Sinn Fein to "hollow out" Britishness in Northern Ireland, and added: "If my party gets this department, this will be returned to you in kind."
Unionist MLAs called for Mr Durkan to see that an option was introduced so people in Northern Ireland could choose whether or not their driving licences displayed the flag.
Alex Easton for the DUP said that he was "hurt that I cannot fly my flag with pride on my driving licence".
Former UUP leader Tom Elliott said: "As a matter of courtesy people should have the option to have the Union flag on their driving licences."
TUV Leader Jim Allister also hit out at Mr Durkan, saying that his actions on the driving licence issue were "inappropriate and wrong-headed".
Mr Allister said that the issue should have been subject to Section 75 equality procedures, and should as a controversial matter have been brought to the Executive.
Nationalist MLAs from the SDLP and Sinn Fein had joined to sign a petition of concern, which guaranteed that the motion would not be passed, but that did not prevent an at times impassioned debate on the flags issue.
Speaker Roy Beggs jnr had some difficulty maintaining order, intervening twice to call for courtesy from MLAs.
Sinn Fein MLA Phil Flanagan attacked the idea of an optional Union flag on driving licences, saying that it would identify the owner's political affiliations.
"It would mark people out, and leave them open for targeting," he said.
He compared the idea to the forced wearing of the Star of David endured by Jews in Nazi Germany.
For Alliance, Anna Lo was also concerned about Northern Ireland licences being different from those in the rest of the UK.
"I can see no compelling case for Northern Ireland to be treated differently " she said.
Mr Durkan put a smile on MLAs' faces when he said that if unionists wanted a Union flag on their licence, they were at liberty to put a sticker on it, and cheekily suggested that Mr Elliott might like to put his over his photograph.
What the minister said
Minister Mark H Durkan sought to calm things down during an at times heated debate over having a Union flag on driving licences. He said that the issuing of licences was a devolved matter and that there had never been a UK-wide driving licence. When the issue of printing a Union flag on the GB licence was raised by London in 2012, he said his predecessor had taken the view that NI licence should not change. Because the status quo was being maintained, Mr Durkan said there was no need to invoke Section 75 Equality procedures, or to bring the matter to the Northern Ireland Executive.