We're looking to install new patio doors and windows (8 in all), and initially looked at companies that do Aluminium and Wood composite windows such as velfac. But anything like that is looking too expensive: can anyone recommend good, high-end uPvc windows that might be a decent substitute, and would work with a 1960s house. Most uPvc windows we've seen are far too chunky.

Sorry I can't help you with a recommendation other than to use a local to you manufacturer/installer rather than the nationals. We did and saved £000s.