Assuming you don't know its name, need more clues as to variety, which is critical to work out when to prune - when it flowers, what colour are the flowers and are they large, open and flat, or small, bellshaped or otherwise? Does it flower May/June, then again later on with smaller flowers? Is it evergreen?

Thanks Bamboo,

I've added a second picture of it in flower. Actually, it's my neighbours plant and she's asked for my help.

Just want to make sure I don't do any permanent damage. :)

It looks like Clematis montana - June is a little late for the flowers, but with the spring we had, that's not really surprising. Unfortunately, this one, if it needs to be kept in check, should be pruned immediately after flowering rather than now - doing it now means either no or very few flowers next year, and hard pruning it now, should we have a hard or early onset winter, will leave it vulnerable to die back or death, depending how long its been in. Your neighbour should really leave it alone, or content herself with a light trim, then do a full, harder pruning after flowering next year. Pruning it back hard might be necessary every year or every other year, given there isn't really enough room for a plant that gets the size of this one over time (35 feet high with a 10/15 foot width)

Thanks for taking the time to reply Bamboo.

Very much appreciated. :)

We'll take your advice.

Mike C.