Got my ILR successfully. I have also found a document from UKBA explaining English Language requirement into detail.
https://www.gov.uk/government/uploads/s ... 5.0EXT.pdf
And the following paragraph from the link explain my situation very well
>> I have already proved my English test by IELTS score when I applied my tier-1. Do I need to re-proved by appear in an exam for ILR?
Validity dates of ESOL qualifications listed in Appendix O of the Immigration Rules, or on the
OFQUAL register, will not be applied for settlement applications, provided:
· the qualification has previously been accepted for another immigration application, or
· if it is being presented for the first time, that it was taken in:
o England and was regulated by OFQUAL
Hope this will help other readers