Yes, 35mm wil be limiting, although when I did my "big trip" years ago that was the widest I had.
Telephoto (70-200) focal lengths are useful both in the countryside (esp. Scotland) and because of the crowds in the cities.
But the main reason I'm posting this is to point out that cities like London and Rome, which I've been to, and probably Paris, which I haven't, don't in fact have tiny narrow streets compared to Australian cities. I don't know Perth, but if you've been to Melbourne that's about as wide as London streets are. Actually, our laneways are narrower than the little Soho streets. Both London and Paris were severely mucked about in the 19th century with wide streets driven through. Additionally, there isn't the overhead electricity wiring we have.
What you will find, in the "high season", are crowds, which tend to push you towards ultra-wide or telephoto focal lengths.