A house does need ventilation. It's incredible how quickly humidity and carbon dioxide build up in an enclosed space from just breathing. The carbon dioxide is bad for you (reduces your ability to concentrate), and the humidity will have to condense out somewhere (on the coldest part of the house, which will usually be the windows, but wherever it is, it'll help mould to grow).
However, getting that ventilation using trickle vents in windows is just a stupid way to do it. You're letting all the heat vent out, and letting the noise in. A better way is with a mechanical ventilation heat recovery (MVHR) system. That sucks air out of some rooms (the bathroom and kitchen are recommended), and passes it through a heat exchanger before pushing it outside, while simultaneously pulling in fresh air from outside, heating it up in the heat exchanger (for free) and blowing it into other rooms (such as bedrooms and the lounge). This is the proper way to do it.
A MVHR system only really makes sense if your house is otherwise fairly non-leaky. However, if you do install it, then it can take over the bathroom and kitchen extraction, and it allows you to plug all those leaks and insulate well, without causing stale air problems.