There were, and are, many hundreds of unregulated border crossing roads and crossing it illegally was never difficult. In the 1970s some roads were cratered to stop vehicle traffic.
I’m a little scared to post this given your deep expertise in these matters, but it was 1707. (I hope. 1st of May 1707 was when the Act of Union came into force, but am worried a small outpost somewhere didn’t ratify it until the next year)
Nothing like that; 1707 is correct. 1708 was a typo. I spotted it, but too late.
It was not until 1923 that customs controls were introduced on the frontier. Part of the Anglo-Irish Treaty established the right of citizens of Ireland and the UK to freely travel between the two countries. At times during ‘The Troubles’, it was easier to catch a ferry from Dublin to Hollyhead than to cross a land border to the North; cars and luggage might be searched etc, but there was no requirement for any identity checks
On the contrary, it was difficult to cross the border illegally because crossing it was not, in itself, illegal. The dense network of border crossings certainly facilitated smuggling, tax and duty evasion, and various other financial/regulatory scams, but not "illegal crossing’.
Much of the preparation work for the Treaty of Union would have been dated 1707 in Scotland but 1706 in England - the new year started in Scotland on January 1st, but in England on March 25th.
Once the two Parliaments had passed the Act, which put into law a treaty already negotiated between commissioners from both parliaments, no ratification by anyone else (small outpost or otherwise) was needed. Which isn’t to say there weren’t some disgruntled people on both sides of the border.
Not even border crossings, I believe. Large parts of the border is just a notional line marked on a map and by little posts here and there.
So you might find the border running down one side of a farm access road, along the wall of a cow shed and then across a couple of fields before swinging off to run down the middle of a stream. The farmer would have to cross the border a dozen times a day just to get his animals to and from the field, spray his weeds, fetch his kids from school etc.
No different from a state border within the US, I would think. Just with the complication of different currencies and a bit of terrorism now and again.
For a long time the pound Irish was pegged to sterling at par, and for the first few years they continued to use English bills and coins as well. The coins stayed the same weight and size, and they occasionally turned in change here (usually low-value ones)
The link was broken when Ireland joined the European Monetary System in 1978, and then completely when the euro started.
Back in the 90s, the Irish Punt exchanged for around 80p. A young man who worked for me made frequent weekend trips, hitchhiking back to his home in Dublin and I asked him one day how he got on with exchanging his cash.
“It’s no problem,” he told me. “Me Ma gives me a straight exchange Pounds for Punts.”
I never told him that his ‘Ma’ was ripping him off.