What incentives can I expect for upgrading to iPhone 5 with O2 at end of contract?

At the end of April 2013, I complete my 24 month contract with O2 and the iPhone 4. At the end of March 2013 I can upgrade to the iPhone 5 a month early.

I see that a new customer can get the iPhone 5 64GB for £209.99 and also have to pay £47 (I currently pay about £43) per month for 24 months, so what incentive can I expect for upgrading rather than just signing up as a new customer or just going elsewhere?

A cheaper iPhone, lower monthly fee or something else?

To be honest the new customer normally gets the better deal, What i would do personally is take a walk to your local o2 shop and see what they are offering it the deal is not to your liking have a look around at the other networks and if you can get a genuine better deal from one of the other networks then go back to o2 and tell them this.
I'm pretty sure they will try and match or better it to keep you with them thats what i have done many times and it normally always work to your advantage.

You won't get much of a deal on that phone as phone companies make very little margin on iPhones. So you can't expect much if any discount on the handset, although they can move a little on the monthly contract fee, but as that still includes a sum to pay back the true cost of the phone it won't be a large discount.

What you can get is more for your money, so more internet, MMS, inclusive minutes (including to 0800, 0845 and similar numbers) and you might even be able to get free accessories or reduced cost insurance.

But you might want to allow your contract to expire and get your existing monthly deal heavily discounted: the iP5 really isn't much of an upgrade over an iP4/4s, and the present deals available for 4G contracts are still very expensive for very limited coverage. The present 4G LTE services are also inferior in terms of signal quality (especially indoors) to the "proper" 4G services launching shortly.