I got my ILR last week based on 5 years work permit through same day service at Solihull Public Enquiry Office.
I had gone through this website before applying for my visa and it really helped me a lot, saved me from paying solicitor fee and to be enough confident that it should all go well...
I booked my appointment online, so if you want a particular branch apply well in advance otherwise you may not get the branch or date you prefer. I think solihull branch is particularly favourite because of staff being friendly and straight forward, that's what I have found on this website in general...
But I think all the offices would give you same level of service anyway...I had worked for the same employer during my 5 years to ILR. I will explain the whole experience below:
I had my appointment for 9:00 at Solihull branch, so reached there well in advance around 8:15, there are different parking places around the office, one across the road and one on the right of the office is John Lewis parking. From outside it is not obvious to find the Public Office, it looks like few terraced houses together and there you would see a small board on the main gate.
They only open the door after 8:30 so you would have to wait patiently outside, may be getting little tensed...
you can go to John Lewis building if you have to go to loo or just to look at your face when you are the most scared in your life for NO REASON... 
They opened the door around 8:45 and I went through airport type security check...
I was the second one in the queue so was called almost within a minute to the counter...
Went to the counter said hello to the officer sitting on the other side of glass window... she was bit serious looking (like most of the immigration officers
but she was nice and straight forward...)Now the list of documents she asked me:
1, Passport
2, Form SET (O) with 2 passport size photo attached
she checked those in like 2 minutes (while my heart was running like jumbo jet...
and then she asked for:3, Life in the UK test
4, Employer letter (which I had got from the sticky on this website)
Then she took 4 minutes going through those documents and my form, again after again while looking at her computer screen... every time I looked on her face she looked more serious...
and after all that time which felt like 400 years to me, she said "sorry my system is bit slow"... when I used to hear this sentence at my work I had never been so relieved, finally I knew that the system is slow and there is nothing wrong in my documents... 
Then she went at the back of the office and came back after a minute or so..
and asked for:
5, My bank statement (I had for last three months)
6, My payslips (I had for last three months)
And then I heard those GOLDEN WORDS.... "Everything is fine with your case and you have been granted ILR"...yippee... when I heard that I thought I had not heard it properly, so I was feeling like asking her again if she has said what I think she has said... but then she said you may now go and pay the fee on next counter...
Finally I came out and hugged my wife, who had tears of joy in her eyes.... so sweet.....
All in all it took me 9 minutes from the moment I was called for my interview to the moment I made my payment.
Then they asked me to come back after 2 hours to collect my passport.
There were few more documents I had taken with me but they never asked for those:
1, P60 (I only had 4, but she never asked for any of those)
2, Excel sheet of days out of UK (wasn't asked for)
3, My initial work permit documents (wasn't asked for)
4, Another letter from employer stating my payslips are genuine (wasn't asked for)
5, Photocopies of all the above documents (I offered her photocopies but she said no, but I think it is always a good idea if you have it since it may just save there time, in case)
In the end it all went well and I was glad to get my ILR. There are few things I have learnt for this process:
1, Only give them (show them) the documents that the officer ask for, if you offer them more it may just raise more questions. Give them answers to the point....
2, Go through your paperwork again and again days before your interview, they may not seem a lot of documents but they are enough to get you ILR. Put them in a sequence and remember the documents by heart.
3, Try to book as early appointment as possible, since in the morning staff is generally relaxed and are not stressed by lots of applications...
If anybody has got any questions I would be more than happy to answer them... sorry for long detail but I thought this website deserves all of this details since it helped me a lot and it might just make life little bit relaxed for some, since I was very worried myself for my ILR...
Thanks everybody and best of luck for your applications...
