Another question about ivy (and clematis)

which clematis?
If its montana, the ivy and that can fight it out between them. The only drawback is that you will need to trim the ivy back twice a year, May and August, to keep it in check once it gets going, and that might be difficult to do with a clematis in it, which won't need cutting then.

hi bamboo. at the moment there are 4 in the area of the new ivy and they are star of india, arabella, sho-un and rhapsody.

Then you'll need to keep the ivy well under control.

Well looks like you've got two definite prune group 3, one prune group 2 and I think Star of India might be 3, but am not certain. Prune group 3 means you cut it down by mid Feb to 2 or 3 buds from the ground, prune group 2, though, shouldn't be cut at all except to nip off tops of dead shots back to healthy buds in March.
Your ivy will need to be cut back twice a year, as I said, normally in early May and then again in August which, when its covered a fence or wall, I'd normally do with a hedgetrimmer. That, though is not going to be possible without cutting all the clematis at the wrong time, so you will be reduced to carefully clipping with shears and secateurs instead, avoiding the stems of any clematis. And good luck with that!!
The answer to your original question, though, is that the clematis will probably be fine if you keep the ivy in severe check.

Oh and Bamboo I have to prune our C montana rubens several times each summer or it would be right over the top of the potting shed roof and down the other side. We always have masses of flowers so it obviously doesn't mind :-)

Good point, but I always hack montanas back immediately after the first flowering anyway, to prevent having to do it later.

I did... then did it twice more :-)

I'd move house!!

Nah we love the garden too much... it isn't difficult to prune back - just grows like a weed!