Section 4.2 of Appendix V,
Immigration Rules says:
The applicant must satisfy the decision maker that they are a genuine visitor. This means that the applicant:
(a) will leave the UK at the end of their visit; and
(b) will not live in the UK for extended periods through frequent or successive visits, or make the UK their main home; and
(c) is genuinely seeking entry for a purpose that is permitted by the visitor routes (these are listed in Appendices 3, 4 and 5); and
(d) will not undertake any prohibited activities set out in V 4.5 – V 4.10; and
(e) must have sufficient funds to cover all reasonable costs in relation to their visit without working or accessing public funds. This includes the cost of the return or onward journey, any costs relating to dependants, and the cost of planned activities such as private medical treatment.
That is generally interpreted (it is not written down anywhere) to mean that the visitor should spend more time in their country of ordinary residence than in the UK. That is the basis of the 6 month in every rolling year rule.
So, it is not whether they are here for 180 days or 183 days, it is whether they are attempting to defeat the purpose and spirit of the Immigration Rules by effectively residing in the UK in the guise of visitors.
The fact that the Immigration Officer noticed that does not bode well for any future visit visa applications. To begin with, that means that there likely is now a note on their Home Office file flagging it up as a potential concern. Secondly, it is worth remembering that an Immigration Officer can cancel a visa that has been issued and can send them back on the next plane back. You are fortunate that the IO did not do that.
I would suggest that after this visa, that they not apply for another visa for a few (5-10) years. You may wish to meet them in either their home country or country of ordinary residence or in another EEA country (which should be visa free if you are a British citizen).
You were similarly advised in
a similar query a year ago.
I am not a lawyer or immigration advisor. My statements/comments do not constitute legal advice. E&OE. Please do not PM me for advice.