How big and what type of tree Bernard?

Either can be grown into trees with greater or lesser success. I have even seen a Golden showers reach the top of a young(ish) Nothofagus antarctica around 25ft heigh as the owners couldn't be bothered to prune it. It flowers quite well every year.

Key things to take into consideration are size and type of tree, do want repeat flowering and do you want vigorous climbing habit?

Ramblers by and large are vigorous, have small flowers held in large sprays and flower en-mass and thats it...spectacular but over within a month-five weeks in early-mid summer.

Climbers are (usually) larger flowered, less vigorous and repeat flower from summer into autumn.

There are a number of ramblers that repeat well with the pale yellow 'Malvern Hills' being probably the best of all and having good scent too.

One you give a little more info including your rose colour preference I may be able to extend this info to help you decide.

I think my keys are sticking or is it just me?.....

Thanks for your response Fractal.
The tree in question is a Silver Birch about 25 years old as are all the other trees in the woodland part of the garden that hasn't developed as well as the others. It is about 30ft high and has a girth of 14" whereas its nearest neighbour is 45ft high with a girth of 35". It seemed therefore that it could benefit from the addition of a climber of some sort. We already have a Clematis montana (white) starting to climb an alder not far away and it seems that if this one had some colour it would be nice. I think repeat flowering would be the first priority with vigour coming second. Even if it takes longer, a climber would eventually reach the same height as a rambler, wouldn't it?
I look forward to your response.

Indeed, many climbers if left to their own devices will eventually get up to a good height (take that Golden Showers I mentioned above). Apart from Zepherine Drouhin (Kathleen Harrop - paler sport of it) which really won't get much above 10ft you are probably not too restricted.

Let me/us know what you decide and I will endeavour to let you know if it should be ok.

Fractal, it seems that a climber would be the best option to go for and I wonder, bearing in mind the enormous variety available, if you would be able to make a recommendation? Would you suggest 'Golden Showers' I wonder - the name is very attractive.

Any of these below would do well and give plenty of growth and repeat flower.

New Dawn, Penny Lane - palest pink or palest peach respectively.

Dublin Bay for a good red.

Pink Perpetue, Albertine.

Madame Alfred Carriere - Ivory white.

Malvern Hills - Pale yellow (repeat flowering rambler).

Summer Wine - open semi-double flowers but great repeating pink/yellow centre.

There are quite a few more varieties of course but the above should all be freely available from most garden centres, especially in autumn if not right now.

ps. Golden Showers - a bit twiggy to be honest and will take a long time to give the growth needed.

Fractal, I'm most grateful to you for your help.