Anyone can take Life in the UK test, I do not see anything stopping anyone.
On the other hand, applying for settlement on a visit visa- well I would say, no chance of success.

It is depend on your status and the age of your parents. If your parents retired and you are British you can apply to be a main caretaker, and they do not have to take a citizenship test.

Subject to your parent's status and age and circumstances, he/she can take Life in the UK test no problem. Is your parent here in the UK as a visitor or is he/shes been your dependant already?

Let me know if i could be of help. My email is don@uklawassociates.co.uk

Do you know if a parent visiting uk can do life in the uk test so that when he/she goes back to home land he/she can apply for ilr from there (or maybe from within uk)??? a reply would be appreciate.

Dear Madam,

I am an immigration lawyer working for ILAS (LLP).
We had few clients in similar position. I just want to comment on possibility of application in country, as there is no ban on switching in relevant immigration rule.

'Indefinite leave to enter or remain as the parent, grandparent or other dependent relative of a person present and settled in the United Kingdom

318. Indefinite leave to enter the United Kingdom as the parent, grandparent or other dependent relative of a person present and settled in the United Kingdom may be granted provided a valid United Kingdom entry clearance for entry in this capacity is produced to the Immigration Officer on arrival. Indefinite leave to remain in the United Kingdom as the parent, grandparent or other dependent relative of a person present and settled in the United Kingdom may be granted provided the Secretary of State is satisfied that each of the requirements of paragraph 317 (i)-(v) is met.'

All our applications were accepted as valid, only one was refused as the evidence of dependency was deemed insufficient.

I found that meeting the requirement of having no other relatives to turn to for support if the applicant has few adult children abroad to be the hardest part of the application.

Should you need professional assistance or advice at any stage of the process, please do not hesitate to contact us.

Immigration and Legal Advisory Services ILAS (LLP) is an immigration firm based in London offering services such as legal advice and representations to UKBA and Tribunals.

We can assist with entry to the UK, extension of stay, permanent residency, regularization of stay and citizenship. We also have an extensive experience in removal and deportation cases and can request for administrative review/reconsideration of decisions, appeals, process applications outside of the rules based on compassionate ground and offer assistance to those in detention.
Our devoted and fully qualified team of in-house lawyers and ex immigration officers, experienced caseworkers and advocates caters for corporate and private immigration applicants and appellants both in the United Kingdom and worldwide.

Please visit our website at www.ilas.org.uk for detailed information about our services.
You may also ring us on (44) (0) 208 539 6611 or alternatively email us on info@ilas.org.uk or ilas@btconnect.com.
Kind regards,
Sylwia Wawrzynczak
On behalf of ILAS (LLP)

Immigration and Legal Advisory Services
Nelson House
341 Lea Bridge Road
London
E10 7LA