Bicycle Mechanics - Top tube not horizontal?

I'm considering buying a used road bike. Everything about it is great; a nice custom Reynolds 853 which is a good fit. There's only one problem. The top tube does not seem to be horizontal. The head tube join is at least 1 cm lower than the seat tube join, ie the direction of the top tube slope is the reverse of the current compact geometry. So I have two questions:
Is this likely to be a significant problem on the road?
If so, is there an easy fix or should I pass on this frame?
Thanks

Depends on how low you like your handlebars. With such a low head tube it will be hard to get the handlebars as high as your average non-track-cyclist/non-racer will find comfortable for anything longer than a couple miles. If you like your handlebars nice and low it seems like it would work.

Sorry if this insults your intelligence, but I have no idea of your knowledge level re this issue.

Are you sure of things such as the size of the mounted wheels - is the front a 650 and the rear a 700, for example? If it is not a custom frame (I saw what you said), it is hard to imagine this anomaly being allowed out of the factory.

OK, I had my morning coffee now, let me try again. :(

1. You said it was custom - who built it?

2. Why do you think the top tube slopes forward? Seems to me that the only way to really tell would be to put the frame in an orientation where the head tube and/or seat tube were around 72 degrees, and then check the level of the top tube.

In addition to my wheel suggestion, it occurs to me that even if the wheels are the same size, if the fork is too short (below the head tube), the same effect would be seen. Therefore point 2 above.

Not sure if 'persuit geometry' could be what the frame was built around?
Fast, uncomfortable.
My triathelon bike frame is the same.
??
Small the front wheel and hit the velodrome!

Thanks for the reply.
I should have said that front and rear wheels are both 700. My judgement about the frame top tube not being horizontal is based on running a plumb line and a spirit level over the frame as the bike stands on a level floor. So yes, you could be right that the fork (standard Columbus Tusk) might produce the impression of the slope from ST to TT. But given that my impression may be correct, my concern was whether this was:
a) Likely to be an error in the frame construction about which I should be concerned, and
b) Whether this geometry is likely to cause any particular ride characteristics about which I should be concerned.
Yours,

So yes, you could be right that the fork (standard Columbus Tusk) might produce the impression of the slope from ST to TT.
I was actually also thinking (if you believe that ;) ) that perhaps the fork had been damaged, shortened at the bottom, and new dropouts installed. Same effect, I would think.

As for ride effects - no clue here.

Good luck.

It's probably a time trial bike and won't be particularly comfortable for long rides.

The "low profile" or low-pro style of frame was used for time trials while back (are these stil UCI-legal?). Is it anything like:

http://www.blackbirdsf.org/bikes/3rensho.html

The old style 3Renshos with the different-sized wheels are no longer legal. Funny bikes with same-sized wheels are legal.

It's probably a time trial bike and won't be particularly comfortable for long rides.
What is specced differently on the frame to make this so?