My parents have come to visit about 5-6 times now, requiring a visa each time, including earlier this year. However, the UK has now (thankfully) removed the visa requirement for Colombians on a short/tourist visit. Having said that, visitors would need to show proof of a place to stay (i.e. hotel reservation) and funds, which is the usual requirement.
For their visa application I've normally sent them a simple letter saying that they would stay with me and my wife at our home and, having the visa, I was always relatively relaxed that they wouldn't have any issues through immigration. They have also been able to prove sufficient funds by themselves, but I could have stepped in if needed.
I'm wondering if now that there is no visa, the same would be sufficient. A cousin who lives in France was having her parents over (Colombians do not need a visa to travel to Shengen countries either), but the lady at the Air France counter at the airport almost didn't let them board because she said that the "plain" invitation letter that they had was insufficient and they needed either a hotel reservation or a certified/notarised letter. Worth noting that for all the grief they gave them at the airport, they were waived through at immigration in Paris

In any case, I know that the UK is different but I'd hate for them to stress out during check-in (or at immigration for that matter) because they don't have a hotel reservation and only have a plain letter. As such, would it be useful to get some sort of certified or notarised letter? Or maybe just send the letter, copy of my passport and copy of the land registry certificate with my name or something like that so that they can print it out?
Maybe being unnecessarily paranoid, but just wondering...
Thanks as always