Krdytkyu

My parents are planning to visit the UK and Europe, and have engaged a tourism company for this. While reviewing the documents they sent us, I noticed that the field asking about friends or relatives in the UK was filled "no". As it happens my parents do have relatives there - an estranged sister and her family. But we haven't managed to contact them and get their details (messages have been ignored).

What information should we submit in this case? The travel agent is recommending that we lie and say we don't have relatives. I feel it would be best to say we do, and fill in the details as best we could (we know the city they live in, but no more), and mark the rest as unknown.

My parents have no intention of going anywhere near them.

Don't lie, regardless of what a travel agent says: it's an immediate family member, not some distant, tangential relation. Include what information they do have (name, city, email etc.). While your parents may not now plan to connect with them while they're in England, they did attempt contact for some reason, and were ignored.

UKVI is adept at spotting discrepancies and a potential refusal for this (deception) would be a serious ding on their immigration records. Your instincts are spot on: the tour company has little to lose, your parents have much more at stake.

Absolutely mention them. Describe your relationship in one word: "estranged". UKVI will get it.

Lying about it is suicide. The typical punishment is not only refusal to enter, which will then make you ineligible for visa waiver, but also bias future visa applications as well. (In the harsher USA, lying is a lifetime ban.)

Also, from immigration's perspective, they are mainly looking for people who want to overstay and seek employ or collect social assistance. Their first impression of lying about a sister is "she is sneaking you in to hire you illegally under the table". They don't know you.

Of course full examination of the facts and circumstances of your lives would debunk that, but that only works for documents you actually submit, and if you send the wrong stuff it could backfire. If you send documents often faked, then that only further prejudices the matter. You never get a second chance to make a first impression.