The UK and EU would like to keep the border frictionless through a comprehensive trade deal.
If such an agreement could not be reached, then to avoid border checks with customs posts or other infrastructure, the backstop would come into force.
It would keep the UK in a “single customs territory” with the EU, and leave Northern Ireland in the EU’s single market for goods.
Many MPs fear the UK could be “trapped” in that arrangement for years, leaving it unable to strike its own trade deals on goods with the rest of the world.
‘Processes and frameworks’
A group of Conservative MPs, the Alternative Arrangements Working Group, is currently exploring possible technical solutions to avoid the backstop.
They have been drawing on the work of a Dutch customs expert Hans Maessen, who suggested a system could be in place within two years.
Mr Henig said it was not just a question of “unproven” technology: “This is about processes, legal frameworks, shared operations.
“These things in my experience, internationally, take a lot of time,” he added.
A legal expert giving evidence to the committee also suggested that the solutions suggested by Mr Maessen do not adequately deal with all the issues.
Colin Murray from Newcastle University said: “There is scant mention of regulation. The solutions you have been presented with do not deal with the complexity of 21st century trade – so much of that lies in non-tariff barriers.”