Niall wrote:
The area in which I am interested is urban photography.
Buildings, people, street entertainers, bridges etc
Here's where you'll need to decide which is most important, and how your shooting habits will play into your choice. If buildings and bridges are most important, then you might want to consider an Ultra Wide angle instead. You can still use your kit lens for shooting people, you'll just need to get closer to them. If however, you intend on sneaking shots, and people are your primary subject of interest, then a long zoom would be most useful.
Either way, it's going to be difficult covering everything with only two lenses, since urban shooting offers such a wide variety of subject matter. There will be times a fast lens is going to be necessary, or you're forced to use a tripod or flash which might not give the best results. Different lenses offer a varied look to your shots due to perspective, & compression abilities. So it seems less than productive to limit yourself to so few.
Is there some reason you feel a need to limit yourself this much now, are you intending to add more glass at a later date? While I always agree that buying "L" glass is the best way to go, if your long term budget is this limited, you might want to consider less expensive alternatives. Only one or two lenses is very restrictive to the creative side of this type of photography. Street shooting is one of the most difficult forms of expression there is, if done properly, and one of the reasons I tend to shy away from it in favor of shooting in more controlled environment and situations.
What I'd suggest is shooting for a few weeks, and see what lens you find yourself wishing you had the most. Try getting closer to people, and further away from buildings/landscapes (If necessary) when shooting to see which you can control the best. Take note of how often you find yourself wanting a faster lens, and how wide/long it needs to be. Once you've learned what's possible with what you have, the answers to what you need tends to be easier to answer for yourself.