By Daniel J. McLaughlin
Currently, when Britain leaves the EU, it will leave behind the customs union with the bloc.
The Irish prime minister argues a customs union would be a "win-win" and that the UK should have a "meaningful" say in trade deals.
However, some argue it would not resolve the Irish border issue and it "loses a lot of its appeal".
Leo Varadkar told the Irish Times that a customs union between the UK and the EU would be a "win-win" for both sides.
He said that Britain should have a "meaningful" say in future European deals. The Irish taoiseach also claimed that a customs union between the UK and the EU would male them "stronger together in dealing with the US, China and Japan".
Varadkar said: “There seems be significant support for the UK forming a customs union with the EU after Brexit. It is of course up to them to decide if that’s what they want and to ask for it.
“But if they do, I think they’d get a favourable response from the European Union. It would make elements of the backstop superfluous and would mean tariff and quota-free trade with Britain for our farmers and agrifood sector."
He added that a customs union would only work if there was a "level playing field" in terms of environmental standards and workers' rights.
However, the New European's Doire Finn argues that a customs union will not solve the Irish border issue.
While it may seem like an attractive idea for parliament, considering they want to avoid both Theresa May's deal and a no-deal Brexit, he argues: "But when you look at it through Northern Irish eyes, it loses a lot of its appeal."
Finn explains: "A customs union doesn’t solve the fundamental conundrum of our invisible border.
"You need to have single market alignment in order to do that as well - if you don’t, you would need to maintain checks on goods.
"Not having checks means that smuggling becomes a lot more attractive: this funnels money to those who come from a darker past, and desire a darker future."
He concludes that a People's Vote is "the only way to save our futures".
When the UK eventually leaves the bloc, pencilled in for October 31, it will leave the customs union. But what exactly is it leaving behind?
According to Politico, there are 15 customs unions worldwide, including the EU customs union and the two less-complete unions between the EU and Turkey and the EU and San Marino.
A customs union simplifies trade between its members. Outside of the EU customs union, for instance, countries have to pay tariffs. A trade agreement - which is what the UK is trying to negotiate - would either reduce or remove those tariffs. And within the union, there are no tariffs at all.
It also reduces administrative and financial trade barriers - including customs checks and charges - between the members of the customs union.
A customs union also removes the need to provide proof of where and how their goods were made - known by the term 'rules of origin' to ensure the correct tariff is levied and that only products from the free trade partner would benefit from the lower tariff.
Full Fact explains: "Different products have different rules agreed between the parties setting out criteria for judging where it came from.
"The average car made in the UK purchases 44 per cent of its components from UK suppliers. But the proportion of this actually made in the UK is somewhere between 20 per cent and 25 per cent.
"For an average free trade agreement (FTA) it would need to meet a 55 to 60 per cent threshold to qualify for whatever reduction in tariffs had been agreed."
The EU customs union, however, prevents members from negotiating their own trade deals elsewhere in the world.