Yes, it's wrong, Penny - they should be pruned immediately after flowering. Any later, and you'll lose the growth which supports the following year's flowers. Pruning information (for any plant) can be found on the RHS's website, an invaluable resource.

having grown this myself, first in a garden where it was left to ramble and cover an area 25 feet by 20 feet, and the next time in a spot where its growth had to be restrained by pruning every other year, I can tell you that the unpruned one flowered prolifically every summer, but the pruned one either didn't flower, or put out a few stems, and I think one year it flowered reasonably well, but nothing like the one left entirely alone.

Thanks Rosie, I have clearly been treating them badly! I will start using the RHS website. After reading Bamboo's observations as well, I think I will remove one plant altogether and leave the other alone for the next year to see what happens! One covering 20' by 25' must have been spectacular in bloom--no chance of that freedom here! Thank you both.
Penny

There was an old ramshackle shed and air raid shelter we weren't allowed to remove (by the owner) so that's why the first one was left to ramble unchecked - it did a brilliant job of covering up all that, and flowered magnificently to boot! But I certainly haven't had that sort of opportunity since...