I have an Indefinite leave to remain (ILR) in UK. However, I have been away from the UK for two years and I need to travel to the UK to visit my son who is a British Citizen. My explicit purpose for visiting is only to see my son and not settle in UK. Can I travel on the ILR/residence permit which has no expiration date? Or has my ILR visa automatically been revoked since I have been away from the UK for more than two years?
You had ILR, but have been outside the UK for 2 years. Now you wish to enter the UK as a FAMILY VISITOR and want to know if your ILR is a viable document for that purpose. You did not say your nationality.
As you're probably aware by now, you cannot benefit from Paragraph 18 of the rules due to this clause
(ii) has not been away from the United Kingdom for more than 2 years; and
If you are NOT a visa-national, you may be able to benefit from Paragraph 19 of the rules, which states
A person who does not benefit from the preceding paragraph by reason only of having been away from the United Kingdom too long may nevertheless be admitted as a returning resident if, for example, he has lived here for most of his life.
...which you can ask for upon arrival (hence, non-visa-nationals only). They apply a demanding test and if you do not qualify you will become vulnerable to being served a removal notice. This can happen if they think you are attempting to enter the UK with the intent of overstaying.
If you are a visa-national, you cannot benefit from Paragraph 19 because you will not be able to board the aircraft without a valid leave to enter.
Alternatively, you can apply from abroad as a 'returning resident'. These applications generally fail, and I wrote an article about why this happens. You can read it here The RRV, Returning Resident Visa. Overall, having a close relative in the UK, such as a son, does not meet the requirement of 'strong family ties' because you have not maintained this relationship for 2 years. The bottom line is that if you opt to apply for the RRV, you should instruct a qualified UK-based practitioner See The Law Society
We believe that submitting an RRV application without competent representation invites peril.
Alternatively, if you are either a visa-national or non-visa-national you can apply for entry clearance as a FAMILY VISITOR. This is the safest approach.
Finally if you are a non-visa-national, you can apply for leave to enter as a FAMILY VISITOR or GENERAL VISITOR upon arrival.
And yes, your ILR has been expired (not 'revoked' or 'cancelled', which are much more serious cases). In all events, it has no purpose other than historical/sentimental value.
The Rules I referred to are here Rules Part 1
The Guidance is here Exceptions to the 2 Year Rule (and especially, whether the person contacted a post abroad within 2 years to express his future intention to return to the United Kingdom. )
Your ILR status is gone, as you have been outside of the UK for two years. If your only intent is visiting your son, then a Short term family visitor visa is probably the best, and cheapest solution for you.
You could also try to get a Returning resident visa, which is basically a revalidation of your ILR.
As you have strong family ties in the UK, you might even get it although you don't plan on settling back. It is a more expensive visa, and they might refuse it (as your intent is not resettlement, but having family ties can be an exception to this rule), but in case you'll get it, you also get your ILR status back as well which might be useful if you plan on visiting your son multiple times in the future.