A photo would help if possible.

Likely to be a sucker - they're usually much more thorny, and the leaves may be a lighter colour, but the real way to confirm it is to trace it back to its point of origin - if its coming from below the graft or bud union at the base, its a sucker, and should be removed, below soil level if necessary.

I'm no rose expert but my Banksia used to throw up vigorous suckers with different leaves and no side shoots. The following year there would be side shoots and the correct leaves. It did look very odd to start with but I think that some ramblers do this?

Bbsmum.....I will try and put a photo on , in-between the lashing raindrops...:((
Thanks Bamboo, yes I remember suckers being almost like a wild briar growing, this is a very thick healthy stem, same amount of thorns, I ws surprised by the 9 leaflets, when I googled it, should be 5 or 7, must be a triffid me thinks!
That's interesting Smorgie, could be that the Rose, being a rambler is sending out long stems for height before allowing it to develop into more normal growth, I know this one does grow up to 30ft and is an old fashioned rambler.