Standard rose growing funny, help please - new gardener

Are the branches of the original crown dead and brown, or are they still green?

I would be inclined to cut off the new crown back down to the level of the old one. This should persuade it to produce new shoots lower down, including from the older branches. If they have died (and you may not know until next spring), then you can create a new crown by pruning your new live shoot.

On the subject of roses - I recently read somewhere that there is a knack to pruning old rose bushes to stop them growing too tall.  Can anybody remember what the tip was?  I have some old roses in the front garden which I cut down to about 12" each spring and they're just growing taller and taller with all the flowers at the top.  Can anybody help pls?

Una.

Generally, the harder you prune the more vigorously the plant will grow. Hence it follows that the rose will grow less if pruned less, although I don't know if that's what you were thinking of.

But some roses will grow tall whatever you do to them - Princess Elizabeth, for example, can get to ten foot.