I really need your guidiance concerning an issue which appears to be my greatest challenge as at of now.

I applied for a Uk visit visa and was given. The visa expires at the end of February. I intend travelling in this month of September as written in my UK application form (just to spend two weeks out of my Annual Leave abroad).
Due to a challenge beyond my control, my leave which was suppose to start on the 15th of September was rescheduled to November by my line manager and i believe that decision is justifiable.

My questions are;

*What would happen if i do not go on the date specified in the application form or what is required of me in this kind of situation cos i intend to reschedule the travelling to November?

*What are the documents needed to be presented at the port of entry?

*I made an hotel reservation for the application but now intend to cancel it cos a friend has agreed to accomodate me for that 2 weeks. Do you think that is possible?

*Finally, i would really want to know those documents required for a visa renewal after expiration. Am i to present those same documents i used for my first application?

Your advise would be so much appreciated.

Thanking you in anticipation of your usual support.

During my visa days, i never travelled to any country on the date i entered in my application form, i always travel later and it was NEVER a problem.
As a bearer of a tourist or visiting visa, i don't think you'd have any problem except you're attending a particular programme with fix dates. What matters is that you don't go to the country before the validity date: any other time is just ok, but avoid going when the visa is close to expiration period, that would be questionable.
  Usually you don't need any document to tender at the port of entry, just your passport,  except your case is complicated.
  As for the accommodation details (hotel), i advice you not to inform the immigration officers at the port of entry that you changed your plans if you don't want them to send you back to Nigeria: just maintain that you're going to lodge in the same given hotel, nobody cares where you eventually stay once you're in the country.

Vicjustice:

During my visa days, i never travelled to any country on the date i entered in my application form, i always travel later and it was NEVER a problem.
As a bearer of a tourist or visiting visa, i don't think you'd have any problem except you're attending a particular programme with fix dates. What matters is that you don't go to the country before the validity date: any other time is just ok, but avoid going when the visa is close to expiration period, that would be questionable.
Usually you don't need any document to tender at the port of entry, just your passport, except your case is complicated.
As for the accommodation details (hotel), i advice you not to inform the immigration officers at the port of entry that you changed your plans if you don't want them to send you back to Nigeria: just maintain that you're going to lodge in the same given hotel, nobody cares where you eventually stay once you're in the country.

Thanks man.
You've pulled a big burden off my head.
I am really grateful for that candid advise.
What is your opinion concerning my last question?

Oh, i forgot to remind you that they might ask for your onward or return ticket (evidence that you're going on to another country or that you intend to return to Nigeria).
As for your question about "visa renewal", DO YOU MEAN VISA EXTENTION?
If so, you have to produce similar documents (not the same with which you obtained the visa because, they might be invalid by the time of extention): you must also produce documents declaring acceptable reasons why you think your visa should be extended.

See my comments below in italics.

*What would happen if i do not go on the date specified in the application form or what is required of me in this kind of situation because i intend to reschedule the travelling to November?

There is no problem with it if you do not go on your specified date. But like Vicjustice mentioned, you should not visit too close to the expiration date of the visa

*What are the documents needed to be presented at the port of entry?

You need your passport, return ticket and a landing card you will fill in the aircraft before you touch down in the UK. Those are compulsory. Make sure your return ticket matches with the period you will be staying in the UK.

*I made an hotel reservation for the application but now intend to cancel it because a friend has agreed to accomodate me for that 2 weeks. Do you think that is possible?

If you will be staying with a friend, make sure you have the exact address details of your friend with you in the aircraft as you will fill the address on the landing card while in the aircraft. You should also be ready to answer basic questions regarding the status of your friend in the UK and what he is doing when the Immigration Officer asks you at the point of entry. Otherwise, rebook the hotel and have the details with you.

*Finally, i would really want to know those documents required for a visa renewal after expiration. Am i to present those same documents i used for my first application?

To renew, just present your documents like you did before, but some of the documents that are variable such as payslips and bank statements should be the most recent ones. Chances are that they will not be used by the high commission since you have travelled before.