Bertie Ahern, Ireland’s taoiseach (prime minister) from 1997 to 2008, said everything must be considered to avoid a hard border.
Mr Ahern, who left a controversy-ridden legacy after his decade in power in Dublin, also urged the European Union to take Theresa May at her word.
He said if the Prime Minister promised there would be no hard border on the island of Ireland, Brussels should accept and respect that.
READ MORE: What does Brexit mean for the Irish border?
Technology should be used to eliminate border checks for most items. For cases in which technology cannot be used, he said, officials should “turn a blind eye”.
He said today: “Theresa May, to take her at her word, she has constantly said she doesn’t want a physical border.
“The EU don’t want a physical border, the Irish government don’t so you are left down with the one alternative: to make technology work in most cases and to turn a blind eye to those areas that can’t come in within technology.”
He said checks could be carried out on larger-scale goods from multi-nationals “back at base”.
But in some instances, a blind eye would have to be turned to keep the border invisible.
He said: ““Some people I talk to tell me that is possible to a great extent but there are some areas where you just have to say it is impossible to check those items.
“I would imagine our economy is relatively small, a huge amount of the trade is multi-nationals, it should be possible I think to do that by technology.
“But of course when you come down to agriculture and smaller items I don’t think technology would work.
“One thing we do not want, can’t have, is back to a physical border.”
The Irish border is the last major obstacle lying in Britain’s way before Brexit talks progress to trade deals and the future relationship between the UK and EU.
Dublin has refused to accept Britain’s lukewarm assurances a hard border will be avoided, saying all proposals are staggeringly deficient in any sort of concrete detail.
This has led to increased frustration in Westminster, where the issue of the border was all-but ignored during the run-up to the referendum last year – despite warnings from leaders in Dublin, Belfast and Brussels.